Nova (1974–…): Season 42, Episode 6 - Hagia Sophia: Istanbul's Mystery - full transcript
Architects and engineers investigate the secrets behind Istanbul's Hagia Sophia, which has survived on one of the world's most active seismic faults since it was built in 537 A.D.
NARRATOR:
Hagia Sophia
For nearly a thousand years,
the largest enclosed building
on earth
Its heavenly dome
soars 180 feet high,
supported by arches
that inspire awe to this day
for their strength
and resilience
When it opened, gold mosaics
covered over four acres
of its walls and ceilings
How did ancient builders
construct
such a magnificent monument?
ROBERT OUSTERHOUT:
There's nothing practical
about Hagia Sophia
It's all innovation
NARRATOR:
Built nearly 1,500 years ago
in Constantinople...
Modern day Istanbul...
Hagia Sophia has survived
clashing empires by transforming
from church to mosque to museum
JOAN BRANHAM:
Hagia Sophia carries
both the history of Christianity
and Islam within its walls
NARRATOR:
Most remarkably,
Hagia Sophia has survived
centuries of city-busting
earthquakes
Did ancient architects
actually design
an earthquake-proof structure?
Or will the next big quake
bring Hagia Sophia down?
To find out, a team of engineers
is monitoring the building
and constructing a giant model,
placing it on
a hydraulic platform,
and hitting it with powerful
simulated earthquakes
Can they unlock Hagia Sophia's
seismic secrets
before Istanbul's next
big quake?
(klaxon blaring)
ESER CAKTI:
There is always
this fear factor,
this fear of seeing
unexpected collapses
Right now on NOVA...
"Hagia Sophia:
Istanbul's Ancient Mystery"
NARRATOR:
Hagia Sophia,
completed in the year 537,
is one of the most magnificent
buildings ever constructed
Its size alone is awe-inspiring
Only the pyramids surpassed it
in height
for almost a thousand years
Its ceiling is a glittering
gold dome
that spans over 100 feet across
and soars 180 feet above
its marble floor
The Statue of Liberty can fit
beneath its dome
with room to spare
How did ancient builders
nearly 1,500 years ago
construct such a gigantic dome?
Since its completion, Hagia
Sophia has withstood
the rise and fall of empires
It has transformed
from Christian church
to Muslim mosque
to secular museum
BRANHAM:
Hagia Sophia influences
a number of mosques
and it became a model for
Christian churches as well
Its innovative, ambitious design
and its monumental scale
speak to people across cultures,
faiths and religions
NARRATOR:
How can one building be a symbol
for two different religions
and continue to inspire people
to this day?
KORAY DURAK:
Hagia Sophia is a unique
building
There are only a few structures
in the world
that present different layers of
history in the last 2,000 years
NARRATOR:
But perhaps the greatest mystery
is why it still stands at all
For Hagia Sophia is in Istanbul,
known as Constantinople
in ancient times
The city straddles two
continents... Europe and Asia...
And a major earthquake fault
Over the last century,
the North Anatolian fault has
unleashed a series of quakes
The most recent, in 1999,
was just 60 miles from Istanbul
And it was devastating,
leveling hundreds of buildings
across the city
and killing thousands of people
MUSTAFA ERDIK:
The damage caused by the '99
earthquake was extensive
Plus, there is a huge
human loss, about
we lost about 17,000 people
NARRATOR:
But somehow, Hagia Sophia
is still standing
In fact, Hagia Sophia has
withstood every major earthquake
for nearly 1,500 years
What is the secret
to its survival?
As Istanbul braces
for the next big one,
a team of engineers searches
for answers
by building an enormous scale
model
and hitting it with a series
of simulated earthquakes
In the process they will uncover
the building's strengths
and weaknesses
weaknesses that could
ultimately threaten
Hagia Sophia's survival
ESER CAKTI:
NARRATOR:
Eser Cakti is director of the
earthquake engineering lab
at Bogazici University
She is tasked with monitoring
the structural integrity
of Hagia Sophia
Slanted floors and leaning
columns may appear alarming
But Cakti is most concerned
about Hagia Sophia's
core structure
That core structure comes down
to a few key elements...
The enormous dome resting on
four huge arches,
which in turn are buttressed
by four giant piers
and two semi-domes
Of particular concern
are the four arches
If any fail,
the dome could collapse
To monitor the arches,
her team has placed sensors
at strategic points
The sensors can detect
the faintest of movements
CAKTI:
The data that we obtain from
here is very important
in terms of understanding the
general structural behavior
of this huge building
NARRATOR:
This information is transmitted
to screens
at Istanbul's Earthquake Center
Each of the multicolored lines
represents vibrations
detected by a motion sensor
Normally the lines
are nearly flat
But when an earthquake strikes,
there's a dramatic spike
From results of years
of monitoring,
Cakti sees two places
of potential danger
CAKTI:
These are the vertical
vibrations on both the arches
on the east and west side
NARRATOR:
Two of the great arches
are moving more than they have
in the past,
which could have serious
implications for the future
If an earthquake
comes strong enough,
I think there is a real chance
it can receive damage
NARRATOR:
Will the next big quake
finally topple Hagia Sophia?
NARRATOR:
To investigate what danger
Hagia Sophia might be in,
Cakti is turning to a tried
and true technique...
A seismic shake table test
It's worked before
In 2012, Cakti teamed up with
engineering team Eren Kalafat
and Korhan Oral to analyze
the structural integrity
of the Mustafa Pasha mosque
in Macedonia
They built this
large-scale model,
placed it on a motorized
steel platform,
then shook it violently
to simulate an earthquake
The idea is that wherever damage
appears on the model
is where damage would appear
on the actual building,
giving engineers important
insights to protect
the real structure
It worked for
the Mustafa Pasha mosque,
but will it work
with Hagia Sophia,
a building larger,
heavier and more complex?
The model team has doubts
The main issue is scale
The core structure must be
precisely scaled down
for the shake table experiment
to be accurate
If Cakti chooses
a scale of 10:1,
the dome, at just over
100 feet wide,
would be 10 feet wide
on the model
But that's still too big
for the shake table
CAKTI:
Each shake table has a capacity
in terms of its dimensions
and in terms of the power
that it can create
NARRATOR:
The capacity of this shake table
is ten tons
The scale Cakti wants to use
will make the model too big,
so she must scale it down
After intense recalculations
it looks like a 26:1 scale
could work, at least on paper
CAKTI:
We are always nervous
at the shake table,
whether it will work
NARRATOR:
The scale model is
an ambitious project
with no guarantee of success
But it pales in comparison
to the challenge of building
the real Hagia Sophia
Who built Hagia Sophia, and why?
Hagia Sophia is built at
a major crossroad in history...
The decline of the Roman Empire
and the rise of
the Byzantine Empire
In 324 A D, after Rome
is ravaged by civil war,
Emperor Constantine establishes
a new capital
in the city of Byzantium
It's renamed after him
He embraces a new religion,
Christianity,
and Constantinople becomes the
center of the Byzantine Empire
as Rome fades in importance
The empire thrives,
but in the early 6th century,
a power struggle erupts after a
new emperor ascends the throne...
Justinian
Riots break out,
challenging his authority
Theodora, his much younger wife
and rumored ex-courtesan,
persuades him to fight
rather than flee
OUSTERHOUT:
Justinian rallied
to the challenge
He called the rebels,
looking as if he was going to
meet their demands,
met them in the hippodrome,
had the doors closed and had
the army slaughter them all
NARRATOR:
Tens of thousands are killed and
Justinian emerges victorious
But during the riots, the rebels
burn down much of the city,
including an older imperial
church also called Hagia Sophia
This is all that remains
OUSTERHOUT:
Much of the city
of Constantinople
had been destroyed
in the great riots,
and this allowed Justinian
the opportunity to, in effect,
rebuild Constantinople and
the church of Hagia Sophia
in his own image
Justinian needed a building to
convey both his power as emperor
and piety as a Christian
So what to build?
Joan Branham is a professor
of art history
at Providence College
and an expert on how builders
design sacred space
She is at San Giovanni
Evangelista,
a church in Ravenna, Italy
Although rebuilt many times,
its floor plan dates
to when Christianity
becomes a state religion
BRANHAM:
For the first few centuries,
Christians worshiped in private,
in homes and small buildings
But this completely changes
in the fourth century
NARRATOR:
Christianity had been
an underground cult
and Christians persecuted
But when Christianity becomes
the official religion
of the Roman Empire, Christians
face a different problem
What should a church look like?
BRANHAM:
Early church builders looked
at Biblical prototypes
like the Temple of Solomon
described in the Hebrew Bible
But it's actually a
secular Roman building
that is adapted for
early Christian use
NARRATOR:
That building is the basilica,
used for courts of law
and other public gatherings
Its floor plan... a large central
nave flanked by two aisles,
and culminating in an apse...
Becomes the model for churches,
an ideal space for worshippers
to gather
Justinian embraces the church's
rectangular shape
to demonstrate his
Christian piety
But he still needs something to
symbolize his imperial power
He looks to the dome of the
Pantheon in Rome,
the ultimate symbol of the might
and glory of the Roman Empire
But the Pantheon's dome sits on
a thick circular base
Justinian wants his dome
to be centered
over a rectangular
Christian basilica
BRANHAM:
Justinian sets out
to do something
that has never been done before
He wanted to merge two
architectural structures
into a mammoth hybrid space
NARRATOR:
So where do you find builders
to create something on a scale
that's never been done before?
Justinian turns
to Greek mathematicians
AHMET CAKMAK:
Justinian hired Anthemius of
Tralles and Isidorus of Miletus
Both had experience as
mathematicians and physicists
and scientists of their day
They were asked to create
the most impressive, biggest
building ever built
NARRATOR:
Justinian puts these university
professors in charge
of 100 contractors
and 10,000 workers,
and gives them the entire
treasury
of the Byzantine Empire
The emperor is taking
a big gamble
OUSTERHOUT:
There's nothing practical
about Hagia Sophia
It's all innovation
It's geometric flights of fancy
beyond what a practical
architect would ever attempt
to build
NARRATOR:
Their first challenge is
how to support the dome
and still keep a huge space
for worshippers below
CAKMAK:
If they built walls or columns,
the space would not be open
like this
It would be much smaller
and narrower
In order to make it as large
and as heavenly as possible,
they need a big space
And that can only be
accomplished
by building large arches
NARRATOR:
A giant dome will need giant
arches to support it
CAKTI:
The original architects should
have been very concerned about
how to support this huge dome
over there
NARRATOR:
The team back at the earthquake
center face the same challenge
building their model
Will their arches be strong
enough to support the dome?
To find out, they add sacks
of cement
to simulate the weight
of the dome
Each bag weighs about 50 pounds,
and they expect the arch
to support about ten of them
But as the fifth bag is placed
Luckily nobody is hurt
as the arch collapses
with only about 200 pounds on it
CAKTI:
It collapsed before
we were expecting
the collapse to take place
I think that happened
because we didn't wait
for the mortar to set fully
NARRATOR:
While this might seem to be
a setback for the team,
Cakti insists this kind of
unanticipated collapse
illustrates one of
the main advantages
of building a physical model
CAKTI:
It is always interesting to see
the failure mechanism
in real life
When you do it on computers,
you develop an idea of how the
failure is going to happen
But it is only during
a test of this kind
where we see the
collapse pattern
NARRATOR:
The slow-motion replay
of the collapse
shows that the downward force
of the sacks
pushes the arch out sideways
The weight of the dome exerts
the same force on the arches
in the real Hagia Sophia
CAKMAK:
The arch wants to push out
and fall down
So you have to hold the arch
together like bookends
NARRATOR:
To create those bookends,
Anthemius and Isidorus,
the Greek mathematicians,
build four buttress piers...
Massive weights of brick and
mortar... and two semi-domes
These push back
against the arches,
canceling out the sideways force
caused by the dome
But Anthemius and Isidorus still
have one more problem to solve:
how to rest the dome on the tips
of the arches
CAKMAK:
The architects had to transition
from a circle to a square
This they accomplished
by building what is called
pendentives
It is this triangular shape
that fills in the corners
of the square
NARRATOR:
The pendentives together
with the arches
transform the circular base of
the dome into a square
And the semi-domes stretch
that square into a rectangle
Justinian has it all...
The classic rectangular shape
of the basilica
capped by the enormous
circular dome
Anthemius and Isidorus complete
Hagia Sophia in only six years
and do indeed spend nearly
the entire treasury
of the Byzantine Empire
In 537, Emperor Justinian
and his wife Theodora
unveil their church to the world
All who enter are awed
by its size
and the richness
of its decorations
Columns crowned by capitals
so finely carved
they look like lace
Floors and walls of marble
dazzle worshippers
with patterns of swirling colors
OUSTERHOUT:
Justinian brought marbles from
all parts of the empire
The great purple columns that we
see in the corners, for example,
come from the imperial quarries
of Egypt
Elsewhere in the building we see
stones brought from as far away
as the Pyrenees in Spain
NARRATOR:
An eyewitness account reports
that the dome looks "as though
it were suspended from heaven
by a golden chain"
Like the church before it,
Justinian christens this
monument "Hagia Sophia,"
which in Greek means
"holy wisdom"
But the dome that Justinian
first sees
is not the same dome that sits
atop Hagia Sophia today
Just 20 years after Hagia
Sophia's unveiling,
its dome collapses in a
catastrophic earthquake
OUSTERHOUT:
We really don't know what
Justinian did
when the first dome collapsed
We can imagine he wasn't
very happy
Fortunately for Isidorus
and Anthemius,
they were dead by that point
CAKMAK:
When the dome collapsed in 558,
the business of rebuilding it
was given to the architect
Isidorus the Younger,
a nephew of the original
architect
NARRATOR:
Cakmak believes Isidorus the
Younger redesigns the dome
To reduce its weight, he
installs 40 windows at its base
CAKMAK:
The windows serve two purposes
One is to get rid of the bricks
that you needed,
which add additional weight,
and to let light in
NARRATOR:
Hagia Sophia is put to the test
in at least another dozen
major earthquakes
The dome suffers two partial
collapses, which were repaired,
so visitors today cast their
eyes up to the same dome
built by Isidorus the Younger
nearly 1,500 years ago
But Hagia Sophia has withstood
more than just seismic activity
It's also been resilient
to cultural upheavals
600 years after Justinian,
Constantinople continues
to flourish,
but its riches inspire envy
In 1204, European Christian
Crusaders on their way
to the Holy Land sack the city
and loot treasures
from the Byzantine Christian
Hagia Sophia
Then a new religion challenges
the old order... Islam
Its forces lay siege to
Constantinople seven times
over eight centuries
Finally, in 1453, Sultan Mehmet
conquers the weakened city
and makes it the capital
of his Ottoman Empire
Mehmet enters the church of
Hagia Sophia on a Tuesday,
and by that Friday he is praying
in the mosque of Hagia Sophia
OUSTERHOUT:
For Mehmet the Conqueror,
Hagia Sophia was really
the ultimate conquest
That was the symbol he was after
for his new empire
NARRATOR:
But how can a church
become a mosque?
From an architectural
perspective, it isn't difficult
BRANHAM:
There was the addition
of the minbar
from which the imam
would give the sermon
The mihrab gave the sacred
direction orientation to Mecca
NARRATOR:
Later, the Ottomans
add large discs
calligraphied with sacred words
from the Koran,
plaster over Christian mosaics,
and outside construct minarets
for the call to prayer
But Hagia Sophia's vast dome
most easily makes the conversion
BRANHAM:
The dome itself had
religious meaning
for both Christian worshippers
and now Muslim worshippers
For both, it was a symbol
of the heavens
The structure at the heart
of Hagia Sophia...
The round dome
on the square base...
Works as powerfully for Islam
as it did for Christianity
Hagia Sophia is so admired
in the Islamic world,
it becomes the classic model
for mosques throughout
the Ottoman Empire
Today, Hagia Sophia is a museum,
a showcase of its religious
and cultural history
DURAK:
When you enter the building,
you look to your left and you
see a beautiful mosaic panel
from the Byzantine Empire
And you look at your right
and you see
a wonderful calligraphic
quotation from the Koran
You see the history
of the whole city,
in a sense the whole region,
in a nutshell
NARRATOR:
But deciding which layers
of its history to display
is a battle that continues
on its walls
Stepping onto the battlefield is
researcher Hitoshi Takanezawa
He's on a hunt for Christian
mosaics that were plastered over
when Hagia Sophia was converted
into a mosque
His challenge is how to find
the Byzantine mosaics
without damaging
the Ottoman decorations
Takanezawa's secret weapon is
this electromagnetic scanner
Normally, it's used to find
structural faults
in things like bridges
Nobody has ever used it
to find Jesus
(speaking Japanese)
HITOSHI TAKANEZAWA (translated):
We're developing new equipment
for investigation
It is crucial we find a
technology that can deduce
whether a mosaic exists without
destroying anything
NARRATOR:
Takanezawa and engineer Satoshi
Baba carefully run the scanner
against the wall
What might they find?
A tantalizing taste
of Hagia Sophia
in its full mosaic splendor
is here,
the church of San Vitale
in Ravenna, Italy,
also built during Justinian's
reign nearly 1,500 years ago
BRANHAM:
Byzantine visitors would be
transported
into an entirely different world
And it was through the mosaics
that this happened
They were a vehicle to bring
the visitor into contact
with the divine
NARRATOR:
That divine glow
of Byzantine mosaics
is what makes them
so awe inspiring
And the mystery material that
gives them that glow
is what will help in the search
for Hagia Sophia's
hidden mosaics
Luciana Notturni
and Gabrielle Warr are using
the same materials to make
mosaics today
They begin with glass discs,
carefully breaking them
into smaller pieces,
until they become tiny cubes
called tesserae
Notturni places each tessera
piece by piece
into a design she's drawn
on the mortar
and carefully angles them
to reflect the light
(speaking Italian)
LUCIANA NOTTURNI (translated):
It is believed
that especially
in the Byzantine mosaics,
the positioning of the tesserae
was directly connected
to where the light was coming
from, so where the windows were,
where the main light sources
were
NARRATOR:
And to make that light shimmer,
they add something else
to the mix
It has a thin layer of gold leaf
And the fact that it does have
gold in it
makes it very reflective
and very luminescent
NARRATOR:
The gold tesserae give
the Byzantine mosaics
a heavenly glow
And because gold is metal,
it may be the key to
rediscovering the lost mosaics
in Hagia Sophia
TAKANEZAWA:
NARRATOR:
Takanezawa's scanner sends
electromagnetic signals
below the surface of the plaster
If the waves strike a buried
metal tessera,
they are reflected back,
creating an image of the inside
of the wall
TAKANEZAWA:
NARRATOR:
The scanner is working
It has detected a mosaic circle
beneath the plaster
But Takanezawa isn't searching
just for circles
TAKANEZAWA:
NARRATOR:
The walls of Hagia Sophia are
hiding more than mosaics
They also hold secrets
to its seismic strength
High above the streets
of Istanbul,
a team is repairing a wall
as part of Hagia Sophia's
ongoing restoration
Sonay Sakar is the lead
architect
(speaking Turkish)
SONAY SAKAR (translated):
What we're doing is removing
all the cement from the surface
you see here
Then we'll repair the layer
of bricks we've uncovered
NARRATOR:
Her team must replace crumbling
cement from a restoration
in the 1950s
She's using a more
resilient mortar,
one formulated from the original
recipe... limestone, sand, water
and a secret ingredient:
ground-up bricks
It turns out the best way to
preserve Hagia Sophia
for the future is to use
materials from the past
SAKAR (translated):
The mortar in Hagia Sophia is
certainly more flexible
than modern mortar
So it adapts to the structural
deformations
caused by earthquakes
NARRATOR:
The flexibility of the mortar
is crucial,
but so is how it's applied
SAKAR (translated):
Hagia Sophia differs
from other structures
because the layer of mortar is
thicker than the bricks
NARRATOR:
Modern brick buildings have thin
layers of mortar,
but Hagia Sophia's layers are so
thick they act like cushioning
Hagia Sophia's bricks also play
a role in earthquake protection
CAKMAK:
Here is an original brick
from Hagia Sophia,
and here is a modern brick
As you can see, the original
brick is significantly lighter
than the modern brick
NARRATOR:
Which turns out to be
very important
CAKMAK:
If you make the weight light,
then the building can sway with
the earthquakes,
like a tree in the wind...
Flexible, but strong
NARRATOR:
1,500 years ago,
other architects built
heavy and massive to protect
against earthquakes
Anthemius and Isidorus,
the Greek architects,
did the opposite
They built light and flexible...
The principle of modern
seismic engineering
But will this world treasure
survive into the future?
Eser Cakti and her team are
building a model
of Hagia Sophia's core structure
to investigate
Their arch problem solved, they
move on to their next challenge:
the semi-domes
They create a mortar
that mimics the materials
of the real semi-domes, and
spread it over a wooden mold
We have worked on paper
for a long time
on how to get it right,
how to make it, and then what
would be the thickness,
what would be the material
NARRATOR:
After the mortar dries,
they remove the wooden mold
But as they take off the mold,
suddenly
a crack appears at the top
Cracks at this stage mean the
semi-dome is clearly too weak
for the shake table test
They break apart the semi-dome
to get a closer look
at the mortar
We have four centimeters coming
from that side
and four centimeters coming
from that side
But the failure part
was too thin
It is almost a half-centimeter
NARRATOR:
A problem with the way
the mortar was applied
caused the top of the semi-dome
to be much thinner than planned
CAKTI:
Some shrinkage occurs after
drying of the mortar
We may consider to introduce
some elements to the mortar
so that its strength properties
will improve
NARRATOR:
The team must rebuild
the semi-dome
And they'll need to come up
with a better method
for building the final piece of
their model...
The large central dome...
And that will take some time
In his hunt for hidden
Byzantine mosaics,
Hitoshi Takanezawa is heading
to the uppermost level
of Hagia Sophia,
a thin ledge that runs beneath
the main arches
The building is so huge,
he must narrow down his search
TAKANEZAWA:
NARRATOR:
Because these niches on the
northern wall are filled
with mosaic figures,
Takanezawa believes the southern
wall may have been too
But have the mosaics survived?
To find out, they run the
electromagnetic scanner
along the wall
TAKANEZAWA:
NARRATOR:
The team takes a closer look
at the scan
They find metal
behind the plaster,
but not the gold
Takanezawa is hoping for
TAKANEZAWA (translated):
There are only horizontal lines
It would seem it is not
a mosaic,
but rather a metal structural
support
NARRATOR:
Takanezawa's guess is wrong;
no mosaics have survived
in this niche
The challenge is
that his scanner measures
about two feet at a time,
and Hagia Sophia's surface area
is over 200,000 square feet
To narrow down his search,
Takanezawa has come to
Bellinzona, Switzerland,
to explore the state archives
Inside, archivist Carlo Agliati
shows him an astonishing record
of Hagia Sophia's
Byzantine mosaics
(speaking Italian)
CARLO AGLIATI (translated):
In 1847, the Sultan entrusted
the architect Gaspare Fossati
with the task of restoring
the mosque of Hagia Sophia
NARRATOR:
These drawings were made
by the Fossati brothers,
Swiss architects who were hired
to renovate the aging building,
which was then a mosque,
in the 1840s
The Fossatis began stripping
plaster from the walls
and were astonished
by what they found
(speaking Italian)
(translated):
Fossati's big discovery during
the restoration,
hidden under the plaster,
was definitely these
extraordinary Byzantine mosaics
NARRATOR:
They quickly documented every
image before covering them
with plaster once again
While some of the mosaics
recorded in the drawings
have been uncovered,
others have never been found
One in particular catches
Takanezawa's eye
(speaking Japanese)
(translated):
There is a circular sketch
from the Fossati,
but the exact location is still
the subject of debate
NARRATOR:
The sketch depicts Christ,
framed by a cross in a circle
Near Hagia Sophia,
the church of Chora
contains a strikingly
similar image
found in the crown of a dome
Takanezawa believes the Fossati
sketch depicts a similar mosaic
in a dome in Hagia Sophia
And he has a hunch
where to find it
(speaking Japanese)
(translated):
A very plausible hypothesis is
that there is a large depiction
of the face of Jesus Christ
at the top of Hagia Sophia's
immense dome
NARRATOR:
But there's a problem
TAKANEZAWA (translated):
Currently it's covered by
plaster and by Koranic verses,
but one day, with our scanner,
we would like to discover
this image
This is my dream
NARRATOR:
It's a dream Takanezawa
could realize
because as part of Hagia
Sophia's ongoing restoration,
this enormous scaffold is about
to reach the dome
But if Takanezawa does
find Christ
beneath the Koranic verse,
what should be shown?
It's a question at the heart of
Hagia Sophia's identity
a question with a long history
CAKMAK:
Religiously, it was
a Greek Orthodox church
And during the Fourth Crusade,
it was taken over,
became a Catholic church
When the Muslims came,
they made it into a mosque
Finally it became a museum,
which we thought was a solution
to the problem
But, unfortunately, the Greeks
would like to make it back
into a church
And the Muslims would like to
make it back into a mosque
And the conflict, controversy
continues
NARRATOR:
But whether Hagia Sophia
remains a museum
or is converted back
to a church or mosque
could prove irrelevant
if there is an earthquake
The more pressing question is
will it be converted
into a pile of rubble?
Eser Cakti hopes the shake table
test will provide some answers
The semi-domes are carefully
rebuilt from mortar
But mortar will be too fragile
for the main dome,
which, like the real thing,
will be built from brick
CAKTI:
We came to the conclusion
that having a brick dome
is much easier to construct
and it's more realistic
So dome-wise, I'm confident
with what will happen
But with respect to the
semi-domes, there I have doubts,
because it's much more fragile
NARRATOR:
Before the test, the seven-ton
model must first survive
the move to the shake table
CAKTI:
This is the largest model ever
to be made in our lab
We need to be very careful
that during lift-up
everything should be perfectly
horizontal
Otherwise, we may damage
the model
NARRATOR:
The model is so heavy
it bends the steel plate
that supports it, which puts
pressure on the structure
It settles onto the shake table,
but has it suffered any damage?
As the wooden molds come away,
Cakti looks for cracks
If the model breaks
at this stage,
they will be unable to perform
the earthquake test
and months of work will have
been for nothing
CAKTI:
Okay, there is some, yeah
We have observed some cracks
on the semi-domes
But we don't see them
from outside
These are just interior cracks
NARRATOR:
Cakti believes the cracks
do not compromise
the structural integrity
of the model
So the team moves on,
installing motion sensors in
similar locations as the sensors
in the real Hagia Sophia
CAKTI:
We will be able to compare
the vibrations
that we record during
the shake table test
with those obtained
from the real structure
NARRATOR:
The model is a scaled-down
version
of Hagia Sophia's core
structure... the main dome,
four great arches, four buttress
piers and the two semi-domes
But will the model move
on the shake table
in a similar way as the real
building moves in an earthquake?
Astonishingly, overnight,
the sensors get an unexpected
trial run: a real earthquake
CAKTI:
At about 4:00 a m
we had an earthquake
near Istanbul
Its magnitude was 3 6
So, by pure chance,
we have now recordings
of that earthquake
recorded on the model
And we have the same earthquake
recorded by our instruments
in Hagia Sophia
NARRATOR:
The parallel recordings verify
that the sensors on the model
and in the real building
are reacting in a similar way
Now it's time to see
how the model will react
to a more powerful quake
(speaking Turkish)
They calibrate the shake table
to simulate the impact
of the devastating '99
earthquake, magnitude 7 4
The duration of the test
is scaled down
to match the size of the model,
about three seconds
The sensors capture every twist
and turn
The model seems to have taken
the impact without damage
But what everyone really wants
to know is how will it stand up
to an even stronger earthquake?
To find out, the team must push
the power of the shake table
beyond anything
they've tried before
The simulated quake
is measured in g's...
Its gravitational force
We are increasing the amplitude
of our earthquake one more step
so that now we aim 2 2 g
You said two was the maximum
Now we are going more than two?
If we can do it,
we'll go for 2 4
Perfect
NARRATOR:
They hit the model
with a simulated earthquake
stronger than any in
Istanbul's recorded history
Cakti checks out the damage
I see one new crack in this arch
But surprisingly, there is
nothing new with the semi-domes
We were afraid about them
But they are as they
have been before
NARRATOR:
The Hagia Sophia model
has survived
two enormous earthquakes in
quick succession,
with minimal damage
But the team isn't done yet
We have passed the known
capacity of our shake table
And then it appears
the mechanics
have allowed us to go further
NARRATOR:
Can the shake table push the
model to the point of collapse?
They hit it with everything
they've got
At this stage, the model has
been hit by the equivalent
of a major earthquake every day
for a week
And although it teeters
on the edge of collapse,
it still stands
There are two vulnerable
parts... the semi-domes
and then the arches
It is just a matter of time to
see which one will go first
NARRATOR:
With everyone's eyes on
the semi-domes and arches,
nobody anticipates
what happens next
The great dome comes
crashing down
I am a little bit surprised now
because I would have expected
the main arch to go,
and then instead of the main
arches, the main dome went
NARRATOR:
The slow-motion replay reveals
that the semi-domes separated
from the structure
and with the main arches
damaged,
support for the dome was
severely compromised
KORHAN ORAL:
My masterpiece is collapsed now
But for scientific observation,
I can accept it
CAKTI:
Now we have come to its end
But, at the same time, we know
that we have lots of things
to do in terms of data analysis
and interpretation
This is a little bit
frightening,
but it needs to be done
NARRATOR:
It is too early to draw
any firm conclusions
But the model going 15 rounds
against the most powerful
simulated earthquakes
the shake table could produce
explains Hagia Sophia's
supposedly miraculous survival
CAKTI:
If there is a miracle,
it is in its design
It was constructed to survive
The balances between its
structural elements
appear to create a dance
The domes, arches, semi-domes,
buttress piers,
they behave in harmony
NARRATOR:
Though the model lies in ruins,
Cakti believes the data captured
in this experiment
will provide new insights
into Hagia Sophia's
structural strength
and how it can be preserved
for the future
OUSTERHOUT:
Scientists have spent decades
trying to analyze the structural
system of Hagia Sophia
But when you go inside
Hagia Sophia today,
you don't see structure
We're not meant to understand
how the great dome is supported
We see only the weightless
quality of the building
That was what was most important
We understand the interior
of the building
as an experience that's
completely different
from anything else on earth
NARRATOR:
After nearly 1,500 years,
Hagia Sophia continues to
astonish modern builders
with its ancient secrets of
seismic engineering,
and for its resilience not
only as a structure,
but also as a symbol
of the great civilizations
that have adopted it
SAKAR (translated):
We don't think of Hagia Sophia
based on the meanings
other people assign to it
Hagia Sophia has an identity
of its own
It is a monumental building;
it is a special building
Our goal is to pass it down
to the next generations
NARRATOR:
Hagia Sophia will have to endure
many more shifts in the ground
that lies beneath it,
and the cultures to which
it is entrusted
Hopefully its majestic beauty
and innovative design
will inspire people of all
religions and cultures
to protect it for generations
to come
Hagia Sophia
For nearly a thousand years,
the largest enclosed building
on earth
Its heavenly dome
soars 180 feet high,
supported by arches
that inspire awe to this day
for their strength
and resilience
When it opened, gold mosaics
covered over four acres
of its walls and ceilings
How did ancient builders
construct
such a magnificent monument?
ROBERT OUSTERHOUT:
There's nothing practical
about Hagia Sophia
It's all innovation
NARRATOR:
Built nearly 1,500 years ago
in Constantinople...
Modern day Istanbul...
Hagia Sophia has survived
clashing empires by transforming
from church to mosque to museum
JOAN BRANHAM:
Hagia Sophia carries
both the history of Christianity
and Islam within its walls
NARRATOR:
Most remarkably,
Hagia Sophia has survived
centuries of city-busting
earthquakes
Did ancient architects
actually design
an earthquake-proof structure?
Or will the next big quake
bring Hagia Sophia down?
To find out, a team of engineers
is monitoring the building
and constructing a giant model,
placing it on
a hydraulic platform,
and hitting it with powerful
simulated earthquakes
Can they unlock Hagia Sophia's
seismic secrets
before Istanbul's next
big quake?
(klaxon blaring)
ESER CAKTI:
There is always
this fear factor,
this fear of seeing
unexpected collapses
Right now on NOVA...
"Hagia Sophia:
Istanbul's Ancient Mystery"
NARRATOR:
Hagia Sophia,
completed in the year 537,
is one of the most magnificent
buildings ever constructed
Its size alone is awe-inspiring
Only the pyramids surpassed it
in height
for almost a thousand years
Its ceiling is a glittering
gold dome
that spans over 100 feet across
and soars 180 feet above
its marble floor
The Statue of Liberty can fit
beneath its dome
with room to spare
How did ancient builders
nearly 1,500 years ago
construct such a gigantic dome?
Since its completion, Hagia
Sophia has withstood
the rise and fall of empires
It has transformed
from Christian church
to Muslim mosque
to secular museum
BRANHAM:
Hagia Sophia influences
a number of mosques
and it became a model for
Christian churches as well
Its innovative, ambitious design
and its monumental scale
speak to people across cultures,
faiths and religions
NARRATOR:
How can one building be a symbol
for two different religions
and continue to inspire people
to this day?
KORAY DURAK:
Hagia Sophia is a unique
building
There are only a few structures
in the world
that present different layers of
history in the last 2,000 years
NARRATOR:
But perhaps the greatest mystery
is why it still stands at all
For Hagia Sophia is in Istanbul,
known as Constantinople
in ancient times
The city straddles two
continents... Europe and Asia...
And a major earthquake fault
Over the last century,
the North Anatolian fault has
unleashed a series of quakes
The most recent, in 1999,
was just 60 miles from Istanbul
And it was devastating,
leveling hundreds of buildings
across the city
and killing thousands of people
MUSTAFA ERDIK:
The damage caused by the '99
earthquake was extensive
Plus, there is a huge
human loss, about
we lost about 17,000 people
NARRATOR:
But somehow, Hagia Sophia
is still standing
In fact, Hagia Sophia has
withstood every major earthquake
for nearly 1,500 years
What is the secret
to its survival?
As Istanbul braces
for the next big one,
a team of engineers searches
for answers
by building an enormous scale
model
and hitting it with a series
of simulated earthquakes
In the process they will uncover
the building's strengths
and weaknesses
weaknesses that could
ultimately threaten
Hagia Sophia's survival
ESER CAKTI:
NARRATOR:
Eser Cakti is director of the
earthquake engineering lab
at Bogazici University
She is tasked with monitoring
the structural integrity
of Hagia Sophia
Slanted floors and leaning
columns may appear alarming
But Cakti is most concerned
about Hagia Sophia's
core structure
That core structure comes down
to a few key elements...
The enormous dome resting on
four huge arches,
which in turn are buttressed
by four giant piers
and two semi-domes
Of particular concern
are the four arches
If any fail,
the dome could collapse
To monitor the arches,
her team has placed sensors
at strategic points
The sensors can detect
the faintest of movements
CAKTI:
The data that we obtain from
here is very important
in terms of understanding the
general structural behavior
of this huge building
NARRATOR:
This information is transmitted
to screens
at Istanbul's Earthquake Center
Each of the multicolored lines
represents vibrations
detected by a motion sensor
Normally the lines
are nearly flat
But when an earthquake strikes,
there's a dramatic spike
From results of years
of monitoring,
Cakti sees two places
of potential danger
CAKTI:
These are the vertical
vibrations on both the arches
on the east and west side
NARRATOR:
Two of the great arches
are moving more than they have
in the past,
which could have serious
implications for the future
If an earthquake
comes strong enough,
I think there is a real chance
it can receive damage
NARRATOR:
Will the next big quake
finally topple Hagia Sophia?
NARRATOR:
To investigate what danger
Hagia Sophia might be in,
Cakti is turning to a tried
and true technique...
A seismic shake table test
It's worked before
In 2012, Cakti teamed up with
engineering team Eren Kalafat
and Korhan Oral to analyze
the structural integrity
of the Mustafa Pasha mosque
in Macedonia
They built this
large-scale model,
placed it on a motorized
steel platform,
then shook it violently
to simulate an earthquake
The idea is that wherever damage
appears on the model
is where damage would appear
on the actual building,
giving engineers important
insights to protect
the real structure
It worked for
the Mustafa Pasha mosque,
but will it work
with Hagia Sophia,
a building larger,
heavier and more complex?
The model team has doubts
The main issue is scale
The core structure must be
precisely scaled down
for the shake table experiment
to be accurate
If Cakti chooses
a scale of 10:1,
the dome, at just over
100 feet wide,
would be 10 feet wide
on the model
But that's still too big
for the shake table
CAKTI:
Each shake table has a capacity
in terms of its dimensions
and in terms of the power
that it can create
NARRATOR:
The capacity of this shake table
is ten tons
The scale Cakti wants to use
will make the model too big,
so she must scale it down
After intense recalculations
it looks like a 26:1 scale
could work, at least on paper
CAKTI:
We are always nervous
at the shake table,
whether it will work
NARRATOR:
The scale model is
an ambitious project
with no guarantee of success
But it pales in comparison
to the challenge of building
the real Hagia Sophia
Who built Hagia Sophia, and why?
Hagia Sophia is built at
a major crossroad in history...
The decline of the Roman Empire
and the rise of
the Byzantine Empire
In 324 A D, after Rome
is ravaged by civil war,
Emperor Constantine establishes
a new capital
in the city of Byzantium
It's renamed after him
He embraces a new religion,
Christianity,
and Constantinople becomes the
center of the Byzantine Empire
as Rome fades in importance
The empire thrives,
but in the early 6th century,
a power struggle erupts after a
new emperor ascends the throne...
Justinian
Riots break out,
challenging his authority
Theodora, his much younger wife
and rumored ex-courtesan,
persuades him to fight
rather than flee
OUSTERHOUT:
Justinian rallied
to the challenge
He called the rebels,
looking as if he was going to
meet their demands,
met them in the hippodrome,
had the doors closed and had
the army slaughter them all
NARRATOR:
Tens of thousands are killed and
Justinian emerges victorious
But during the riots, the rebels
burn down much of the city,
including an older imperial
church also called Hagia Sophia
This is all that remains
OUSTERHOUT:
Much of the city
of Constantinople
had been destroyed
in the great riots,
and this allowed Justinian
the opportunity to, in effect,
rebuild Constantinople and
the church of Hagia Sophia
in his own image
Justinian needed a building to
convey both his power as emperor
and piety as a Christian
So what to build?
Joan Branham is a professor
of art history
at Providence College
and an expert on how builders
design sacred space
She is at San Giovanni
Evangelista,
a church in Ravenna, Italy
Although rebuilt many times,
its floor plan dates
to when Christianity
becomes a state religion
BRANHAM:
For the first few centuries,
Christians worshiped in private,
in homes and small buildings
But this completely changes
in the fourth century
NARRATOR:
Christianity had been
an underground cult
and Christians persecuted
But when Christianity becomes
the official religion
of the Roman Empire, Christians
face a different problem
What should a church look like?
BRANHAM:
Early church builders looked
at Biblical prototypes
like the Temple of Solomon
described in the Hebrew Bible
But it's actually a
secular Roman building
that is adapted for
early Christian use
NARRATOR:
That building is the basilica,
used for courts of law
and other public gatherings
Its floor plan... a large central
nave flanked by two aisles,
and culminating in an apse...
Becomes the model for churches,
an ideal space for worshippers
to gather
Justinian embraces the church's
rectangular shape
to demonstrate his
Christian piety
But he still needs something to
symbolize his imperial power
He looks to the dome of the
Pantheon in Rome,
the ultimate symbol of the might
and glory of the Roman Empire
But the Pantheon's dome sits on
a thick circular base
Justinian wants his dome
to be centered
over a rectangular
Christian basilica
BRANHAM:
Justinian sets out
to do something
that has never been done before
He wanted to merge two
architectural structures
into a mammoth hybrid space
NARRATOR:
So where do you find builders
to create something on a scale
that's never been done before?
Justinian turns
to Greek mathematicians
AHMET CAKMAK:
Justinian hired Anthemius of
Tralles and Isidorus of Miletus
Both had experience as
mathematicians and physicists
and scientists of their day
They were asked to create
the most impressive, biggest
building ever built
NARRATOR:
Justinian puts these university
professors in charge
of 100 contractors
and 10,000 workers,
and gives them the entire
treasury
of the Byzantine Empire
The emperor is taking
a big gamble
OUSTERHOUT:
There's nothing practical
about Hagia Sophia
It's all innovation
It's geometric flights of fancy
beyond what a practical
architect would ever attempt
to build
NARRATOR:
Their first challenge is
how to support the dome
and still keep a huge space
for worshippers below
CAKMAK:
If they built walls or columns,
the space would not be open
like this
It would be much smaller
and narrower
In order to make it as large
and as heavenly as possible,
they need a big space
And that can only be
accomplished
by building large arches
NARRATOR:
A giant dome will need giant
arches to support it
CAKTI:
The original architects should
have been very concerned about
how to support this huge dome
over there
NARRATOR:
The team back at the earthquake
center face the same challenge
building their model
Will their arches be strong
enough to support the dome?
To find out, they add sacks
of cement
to simulate the weight
of the dome
Each bag weighs about 50 pounds,
and they expect the arch
to support about ten of them
But as the fifth bag is placed
Luckily nobody is hurt
as the arch collapses
with only about 200 pounds on it
CAKTI:
It collapsed before
we were expecting
the collapse to take place
I think that happened
because we didn't wait
for the mortar to set fully
NARRATOR:
While this might seem to be
a setback for the team,
Cakti insists this kind of
unanticipated collapse
illustrates one of
the main advantages
of building a physical model
CAKTI:
It is always interesting to see
the failure mechanism
in real life
When you do it on computers,
you develop an idea of how the
failure is going to happen
But it is only during
a test of this kind
where we see the
collapse pattern
NARRATOR:
The slow-motion replay
of the collapse
shows that the downward force
of the sacks
pushes the arch out sideways
The weight of the dome exerts
the same force on the arches
in the real Hagia Sophia
CAKMAK:
The arch wants to push out
and fall down
So you have to hold the arch
together like bookends
NARRATOR:
To create those bookends,
Anthemius and Isidorus,
the Greek mathematicians,
build four buttress piers...
Massive weights of brick and
mortar... and two semi-domes
These push back
against the arches,
canceling out the sideways force
caused by the dome
But Anthemius and Isidorus still
have one more problem to solve:
how to rest the dome on the tips
of the arches
CAKMAK:
The architects had to transition
from a circle to a square
This they accomplished
by building what is called
pendentives
It is this triangular shape
that fills in the corners
of the square
NARRATOR:
The pendentives together
with the arches
transform the circular base of
the dome into a square
And the semi-domes stretch
that square into a rectangle
Justinian has it all...
The classic rectangular shape
of the basilica
capped by the enormous
circular dome
Anthemius and Isidorus complete
Hagia Sophia in only six years
and do indeed spend nearly
the entire treasury
of the Byzantine Empire
In 537, Emperor Justinian
and his wife Theodora
unveil their church to the world
All who enter are awed
by its size
and the richness
of its decorations
Columns crowned by capitals
so finely carved
they look like lace
Floors and walls of marble
dazzle worshippers
with patterns of swirling colors
OUSTERHOUT:
Justinian brought marbles from
all parts of the empire
The great purple columns that we
see in the corners, for example,
come from the imperial quarries
of Egypt
Elsewhere in the building we see
stones brought from as far away
as the Pyrenees in Spain
NARRATOR:
An eyewitness account reports
that the dome looks "as though
it were suspended from heaven
by a golden chain"
Like the church before it,
Justinian christens this
monument "Hagia Sophia,"
which in Greek means
"holy wisdom"
But the dome that Justinian
first sees
is not the same dome that sits
atop Hagia Sophia today
Just 20 years after Hagia
Sophia's unveiling,
its dome collapses in a
catastrophic earthquake
OUSTERHOUT:
We really don't know what
Justinian did
when the first dome collapsed
We can imagine he wasn't
very happy
Fortunately for Isidorus
and Anthemius,
they were dead by that point
CAKMAK:
When the dome collapsed in 558,
the business of rebuilding it
was given to the architect
Isidorus the Younger,
a nephew of the original
architect
NARRATOR:
Cakmak believes Isidorus the
Younger redesigns the dome
To reduce its weight, he
installs 40 windows at its base
CAKMAK:
The windows serve two purposes
One is to get rid of the bricks
that you needed,
which add additional weight,
and to let light in
NARRATOR:
Hagia Sophia is put to the test
in at least another dozen
major earthquakes
The dome suffers two partial
collapses, which were repaired,
so visitors today cast their
eyes up to the same dome
built by Isidorus the Younger
nearly 1,500 years ago
But Hagia Sophia has withstood
more than just seismic activity
It's also been resilient
to cultural upheavals
600 years after Justinian,
Constantinople continues
to flourish,
but its riches inspire envy
In 1204, European Christian
Crusaders on their way
to the Holy Land sack the city
and loot treasures
from the Byzantine Christian
Hagia Sophia
Then a new religion challenges
the old order... Islam
Its forces lay siege to
Constantinople seven times
over eight centuries
Finally, in 1453, Sultan Mehmet
conquers the weakened city
and makes it the capital
of his Ottoman Empire
Mehmet enters the church of
Hagia Sophia on a Tuesday,
and by that Friday he is praying
in the mosque of Hagia Sophia
OUSTERHOUT:
For Mehmet the Conqueror,
Hagia Sophia was really
the ultimate conquest
That was the symbol he was after
for his new empire
NARRATOR:
But how can a church
become a mosque?
From an architectural
perspective, it isn't difficult
BRANHAM:
There was the addition
of the minbar
from which the imam
would give the sermon
The mihrab gave the sacred
direction orientation to Mecca
NARRATOR:
Later, the Ottomans
add large discs
calligraphied with sacred words
from the Koran,
plaster over Christian mosaics,
and outside construct minarets
for the call to prayer
But Hagia Sophia's vast dome
most easily makes the conversion
BRANHAM:
The dome itself had
religious meaning
for both Christian worshippers
and now Muslim worshippers
For both, it was a symbol
of the heavens
The structure at the heart
of Hagia Sophia...
The round dome
on the square base...
Works as powerfully for Islam
as it did for Christianity
Hagia Sophia is so admired
in the Islamic world,
it becomes the classic model
for mosques throughout
the Ottoman Empire
Today, Hagia Sophia is a museum,
a showcase of its religious
and cultural history
DURAK:
When you enter the building,
you look to your left and you
see a beautiful mosaic panel
from the Byzantine Empire
And you look at your right
and you see
a wonderful calligraphic
quotation from the Koran
You see the history
of the whole city,
in a sense the whole region,
in a nutshell
NARRATOR:
But deciding which layers
of its history to display
is a battle that continues
on its walls
Stepping onto the battlefield is
researcher Hitoshi Takanezawa
He's on a hunt for Christian
mosaics that were plastered over
when Hagia Sophia was converted
into a mosque
His challenge is how to find
the Byzantine mosaics
without damaging
the Ottoman decorations
Takanezawa's secret weapon is
this electromagnetic scanner
Normally, it's used to find
structural faults
in things like bridges
Nobody has ever used it
to find Jesus
(speaking Japanese)
HITOSHI TAKANEZAWA (translated):
We're developing new equipment
for investigation
It is crucial we find a
technology that can deduce
whether a mosaic exists without
destroying anything
NARRATOR:
Takanezawa and engineer Satoshi
Baba carefully run the scanner
against the wall
What might they find?
A tantalizing taste
of Hagia Sophia
in its full mosaic splendor
is here,
the church of San Vitale
in Ravenna, Italy,
also built during Justinian's
reign nearly 1,500 years ago
BRANHAM:
Byzantine visitors would be
transported
into an entirely different world
And it was through the mosaics
that this happened
They were a vehicle to bring
the visitor into contact
with the divine
NARRATOR:
That divine glow
of Byzantine mosaics
is what makes them
so awe inspiring
And the mystery material that
gives them that glow
is what will help in the search
for Hagia Sophia's
hidden mosaics
Luciana Notturni
and Gabrielle Warr are using
the same materials to make
mosaics today
They begin with glass discs,
carefully breaking them
into smaller pieces,
until they become tiny cubes
called tesserae
Notturni places each tessera
piece by piece
into a design she's drawn
on the mortar
and carefully angles them
to reflect the light
(speaking Italian)
LUCIANA NOTTURNI (translated):
It is believed
that especially
in the Byzantine mosaics,
the positioning of the tesserae
was directly connected
to where the light was coming
from, so where the windows were,
where the main light sources
were
NARRATOR:
And to make that light shimmer,
they add something else
to the mix
It has a thin layer of gold leaf
And the fact that it does have
gold in it
makes it very reflective
and very luminescent
NARRATOR:
The gold tesserae give
the Byzantine mosaics
a heavenly glow
And because gold is metal,
it may be the key to
rediscovering the lost mosaics
in Hagia Sophia
TAKANEZAWA:
NARRATOR:
Takanezawa's scanner sends
electromagnetic signals
below the surface of the plaster
If the waves strike a buried
metal tessera,
they are reflected back,
creating an image of the inside
of the wall
TAKANEZAWA:
NARRATOR:
The scanner is working
It has detected a mosaic circle
beneath the plaster
But Takanezawa isn't searching
just for circles
TAKANEZAWA:
NARRATOR:
The walls of Hagia Sophia are
hiding more than mosaics
They also hold secrets
to its seismic strength
High above the streets
of Istanbul,
a team is repairing a wall
as part of Hagia Sophia's
ongoing restoration
Sonay Sakar is the lead
architect
(speaking Turkish)
SONAY SAKAR (translated):
What we're doing is removing
all the cement from the surface
you see here
Then we'll repair the layer
of bricks we've uncovered
NARRATOR:
Her team must replace crumbling
cement from a restoration
in the 1950s
She's using a more
resilient mortar,
one formulated from the original
recipe... limestone, sand, water
and a secret ingredient:
ground-up bricks
It turns out the best way to
preserve Hagia Sophia
for the future is to use
materials from the past
SAKAR (translated):
The mortar in Hagia Sophia is
certainly more flexible
than modern mortar
So it adapts to the structural
deformations
caused by earthquakes
NARRATOR:
The flexibility of the mortar
is crucial,
but so is how it's applied
SAKAR (translated):
Hagia Sophia differs
from other structures
because the layer of mortar is
thicker than the bricks
NARRATOR:
Modern brick buildings have thin
layers of mortar,
but Hagia Sophia's layers are so
thick they act like cushioning
Hagia Sophia's bricks also play
a role in earthquake protection
CAKMAK:
Here is an original brick
from Hagia Sophia,
and here is a modern brick
As you can see, the original
brick is significantly lighter
than the modern brick
NARRATOR:
Which turns out to be
very important
CAKMAK:
If you make the weight light,
then the building can sway with
the earthquakes,
like a tree in the wind...
Flexible, but strong
NARRATOR:
1,500 years ago,
other architects built
heavy and massive to protect
against earthquakes
Anthemius and Isidorus,
the Greek architects,
did the opposite
They built light and flexible...
The principle of modern
seismic engineering
But will this world treasure
survive into the future?
Eser Cakti and her team are
building a model
of Hagia Sophia's core structure
to investigate
Their arch problem solved, they
move on to their next challenge:
the semi-domes
They create a mortar
that mimics the materials
of the real semi-domes, and
spread it over a wooden mold
We have worked on paper
for a long time
on how to get it right,
how to make it, and then what
would be the thickness,
what would be the material
NARRATOR:
After the mortar dries,
they remove the wooden mold
But as they take off the mold,
suddenly
a crack appears at the top
Cracks at this stage mean the
semi-dome is clearly too weak
for the shake table test
They break apart the semi-dome
to get a closer look
at the mortar
We have four centimeters coming
from that side
and four centimeters coming
from that side
But the failure part
was too thin
It is almost a half-centimeter
NARRATOR:
A problem with the way
the mortar was applied
caused the top of the semi-dome
to be much thinner than planned
CAKTI:
Some shrinkage occurs after
drying of the mortar
We may consider to introduce
some elements to the mortar
so that its strength properties
will improve
NARRATOR:
The team must rebuild
the semi-dome
And they'll need to come up
with a better method
for building the final piece of
their model...
The large central dome...
And that will take some time
In his hunt for hidden
Byzantine mosaics,
Hitoshi Takanezawa is heading
to the uppermost level
of Hagia Sophia,
a thin ledge that runs beneath
the main arches
The building is so huge,
he must narrow down his search
TAKANEZAWA:
NARRATOR:
Because these niches on the
northern wall are filled
with mosaic figures,
Takanezawa believes the southern
wall may have been too
But have the mosaics survived?
To find out, they run the
electromagnetic scanner
along the wall
TAKANEZAWA:
NARRATOR:
The team takes a closer look
at the scan
They find metal
behind the plaster,
but not the gold
Takanezawa is hoping for
TAKANEZAWA (translated):
There are only horizontal lines
It would seem it is not
a mosaic,
but rather a metal structural
support
NARRATOR:
Takanezawa's guess is wrong;
no mosaics have survived
in this niche
The challenge is
that his scanner measures
about two feet at a time,
and Hagia Sophia's surface area
is over 200,000 square feet
To narrow down his search,
Takanezawa has come to
Bellinzona, Switzerland,
to explore the state archives
Inside, archivist Carlo Agliati
shows him an astonishing record
of Hagia Sophia's
Byzantine mosaics
(speaking Italian)
CARLO AGLIATI (translated):
In 1847, the Sultan entrusted
the architect Gaspare Fossati
with the task of restoring
the mosque of Hagia Sophia
NARRATOR:
These drawings were made
by the Fossati brothers,
Swiss architects who were hired
to renovate the aging building,
which was then a mosque,
in the 1840s
The Fossatis began stripping
plaster from the walls
and were astonished
by what they found
(speaking Italian)
(translated):
Fossati's big discovery during
the restoration,
hidden under the plaster,
was definitely these
extraordinary Byzantine mosaics
NARRATOR:
They quickly documented every
image before covering them
with plaster once again
While some of the mosaics
recorded in the drawings
have been uncovered,
others have never been found
One in particular catches
Takanezawa's eye
(speaking Japanese)
(translated):
There is a circular sketch
from the Fossati,
but the exact location is still
the subject of debate
NARRATOR:
The sketch depicts Christ,
framed by a cross in a circle
Near Hagia Sophia,
the church of Chora
contains a strikingly
similar image
found in the crown of a dome
Takanezawa believes the Fossati
sketch depicts a similar mosaic
in a dome in Hagia Sophia
And he has a hunch
where to find it
(speaking Japanese)
(translated):
A very plausible hypothesis is
that there is a large depiction
of the face of Jesus Christ
at the top of Hagia Sophia's
immense dome
NARRATOR:
But there's a problem
TAKANEZAWA (translated):
Currently it's covered by
plaster and by Koranic verses,
but one day, with our scanner,
we would like to discover
this image
This is my dream
NARRATOR:
It's a dream Takanezawa
could realize
because as part of Hagia
Sophia's ongoing restoration,
this enormous scaffold is about
to reach the dome
But if Takanezawa does
find Christ
beneath the Koranic verse,
what should be shown?
It's a question at the heart of
Hagia Sophia's identity
a question with a long history
CAKMAK:
Religiously, it was
a Greek Orthodox church
And during the Fourth Crusade,
it was taken over,
became a Catholic church
When the Muslims came,
they made it into a mosque
Finally it became a museum,
which we thought was a solution
to the problem
But, unfortunately, the Greeks
would like to make it back
into a church
And the Muslims would like to
make it back into a mosque
And the conflict, controversy
continues
NARRATOR:
But whether Hagia Sophia
remains a museum
or is converted back
to a church or mosque
could prove irrelevant
if there is an earthquake
The more pressing question is
will it be converted
into a pile of rubble?
Eser Cakti hopes the shake table
test will provide some answers
The semi-domes are carefully
rebuilt from mortar
But mortar will be too fragile
for the main dome,
which, like the real thing,
will be built from brick
CAKTI:
We came to the conclusion
that having a brick dome
is much easier to construct
and it's more realistic
So dome-wise, I'm confident
with what will happen
But with respect to the
semi-domes, there I have doubts,
because it's much more fragile
NARRATOR:
Before the test, the seven-ton
model must first survive
the move to the shake table
CAKTI:
This is the largest model ever
to be made in our lab
We need to be very careful
that during lift-up
everything should be perfectly
horizontal
Otherwise, we may damage
the model
NARRATOR:
The model is so heavy
it bends the steel plate
that supports it, which puts
pressure on the structure
It settles onto the shake table,
but has it suffered any damage?
As the wooden molds come away,
Cakti looks for cracks
If the model breaks
at this stage,
they will be unable to perform
the earthquake test
and months of work will have
been for nothing
CAKTI:
Okay, there is some, yeah
We have observed some cracks
on the semi-domes
But we don't see them
from outside
These are just interior cracks
NARRATOR:
Cakti believes the cracks
do not compromise
the structural integrity
of the model
So the team moves on,
installing motion sensors in
similar locations as the sensors
in the real Hagia Sophia
CAKTI:
We will be able to compare
the vibrations
that we record during
the shake table test
with those obtained
from the real structure
NARRATOR:
The model is a scaled-down
version
of Hagia Sophia's core
structure... the main dome,
four great arches, four buttress
piers and the two semi-domes
But will the model move
on the shake table
in a similar way as the real
building moves in an earthquake?
Astonishingly, overnight,
the sensors get an unexpected
trial run: a real earthquake
CAKTI:
At about 4:00 a m
we had an earthquake
near Istanbul
Its magnitude was 3 6
So, by pure chance,
we have now recordings
of that earthquake
recorded on the model
And we have the same earthquake
recorded by our instruments
in Hagia Sophia
NARRATOR:
The parallel recordings verify
that the sensors on the model
and in the real building
are reacting in a similar way
Now it's time to see
how the model will react
to a more powerful quake
(speaking Turkish)
They calibrate the shake table
to simulate the impact
of the devastating '99
earthquake, magnitude 7 4
The duration of the test
is scaled down
to match the size of the model,
about three seconds
The sensors capture every twist
and turn
The model seems to have taken
the impact without damage
But what everyone really wants
to know is how will it stand up
to an even stronger earthquake?
To find out, the team must push
the power of the shake table
beyond anything
they've tried before
The simulated quake
is measured in g's...
Its gravitational force
We are increasing the amplitude
of our earthquake one more step
so that now we aim 2 2 g
You said two was the maximum
Now we are going more than two?
If we can do it,
we'll go for 2 4
Perfect
NARRATOR:
They hit the model
with a simulated earthquake
stronger than any in
Istanbul's recorded history
Cakti checks out the damage
I see one new crack in this arch
But surprisingly, there is
nothing new with the semi-domes
We were afraid about them
But they are as they
have been before
NARRATOR:
The Hagia Sophia model
has survived
two enormous earthquakes in
quick succession,
with minimal damage
But the team isn't done yet
We have passed the known
capacity of our shake table
And then it appears
the mechanics
have allowed us to go further
NARRATOR:
Can the shake table push the
model to the point of collapse?
They hit it with everything
they've got
At this stage, the model has
been hit by the equivalent
of a major earthquake every day
for a week
And although it teeters
on the edge of collapse,
it still stands
There are two vulnerable
parts... the semi-domes
and then the arches
It is just a matter of time to
see which one will go first
NARRATOR:
With everyone's eyes on
the semi-domes and arches,
nobody anticipates
what happens next
The great dome comes
crashing down
I am a little bit surprised now
because I would have expected
the main arch to go,
and then instead of the main
arches, the main dome went
NARRATOR:
The slow-motion replay reveals
that the semi-domes separated
from the structure
and with the main arches
damaged,
support for the dome was
severely compromised
KORHAN ORAL:
My masterpiece is collapsed now
But for scientific observation,
I can accept it
CAKTI:
Now we have come to its end
But, at the same time, we know
that we have lots of things
to do in terms of data analysis
and interpretation
This is a little bit
frightening,
but it needs to be done
NARRATOR:
It is too early to draw
any firm conclusions
But the model going 15 rounds
against the most powerful
simulated earthquakes
the shake table could produce
explains Hagia Sophia's
supposedly miraculous survival
CAKTI:
If there is a miracle,
it is in its design
It was constructed to survive
The balances between its
structural elements
appear to create a dance
The domes, arches, semi-domes,
buttress piers,
they behave in harmony
NARRATOR:
Though the model lies in ruins,
Cakti believes the data captured
in this experiment
will provide new insights
into Hagia Sophia's
structural strength
and how it can be preserved
for the future
OUSTERHOUT:
Scientists have spent decades
trying to analyze the structural
system of Hagia Sophia
But when you go inside
Hagia Sophia today,
you don't see structure
We're not meant to understand
how the great dome is supported
We see only the weightless
quality of the building
That was what was most important
We understand the interior
of the building
as an experience that's
completely different
from anything else on earth
NARRATOR:
After nearly 1,500 years,
Hagia Sophia continues to
astonish modern builders
with its ancient secrets of
seismic engineering,
and for its resilience not
only as a structure,
but also as a symbol
of the great civilizations
that have adopted it
SAKAR (translated):
We don't think of Hagia Sophia
based on the meanings
other people assign to it
Hagia Sophia has an identity
of its own
It is a monumental building;
it is a special building
Our goal is to pass it down
to the next generations
NARRATOR:
Hagia Sophia will have to endure
many more shifts in the ground
that lies beneath it,
and the cultures to which
it is entrusted
Hopefully its majestic beauty
and innovative design
will inspire people of all
religions and cultures
to protect it for generations
to come