Big ancient Domes

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October 19th 2012
Published: October 19th 2012
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The Pantheon in RomeThe Pantheon in RomeThe Pantheon in Rome

This is the oldest large dome in the world, constructed under Hadrian.
Big Ancient Domes

After an hour and a half in Topkapi, we walked to the Hagia Sophia, then on to the Blue Mosque, then on to the Grand Bazaar. They are all very close together, but it makes for a day so full of things that it is hard to remember accurately, even today as I write it up a few weeks later. The sequential photos from my camera help.

The Hagia Sophia brought up some thoughts about the big domes we have seen on our travels. Let's start with the Pantheon in Rome, the oldest unruined building in the world. It was built by Hadrian as a temple for All the Gods in 126 AD. It has a huge dome; a sphere 142 feet in diameter would fit snugly inside it. It has a hole at the top to let in sunlight and rainwater. I attach an aerial photo of it; it has a very simple design.

Why has it survived? First, the dome is remakably light. It is honeycombed with cavities, and uses stone of decreasing density, up to actual pumice stone near the top. Also the hole lightens it
Hagia Sophia from the airHagia Sophia from the airHagia Sophia from the air

Observe how the main dome and the two half domes fit together to roof over an oblong space
considerably. Second, Rome is remarkably stable against earthquakes- no one has ever been killed by a quake inside the old walls of Rome. Its few minor quakes originate in the Apennines, over 50 miles away, with a maximum strength in Rome of 6.0. So there the Pantheon stands, 1,886 years old in this year, 2012. It must be under the protection of All the Gods, both ancient and modern.

The second oldest big dome in the world is the Hagia Sophia, built by Justinian I in 537 AD. The main dome is 102 feet in diameter. It is flanked by two half domes, that cover together a rectangular space of 102 feet by 265 feet. The aerial photograph that shows how the main dome and the two half domes fit together.

Sophia has not been as lucky as the Pantheon, because of design errors and because of repeated severe earthquakes. The original dome was too flat, and it soon pushed the its supports out of vertical. Then it collapsed completely in a quake 21 years after it was built. Justinian immediately straightened the supports and rebuilt the dome 60 feet higher, and with lighter
The Sagrada Familia, BarcelonaThe Sagrada Familia, BarcelonaThe Sagrada Familia, Barcelona

The catenary domes of the Sagrada Familia exert no sideways forces on their supports. But they cannot roof over a very large space, so there are a lot of them.
materials. Therefore it pushed more downward and less outward on the supports.

Then in 869 another quake collapsed one of the half domes (again rebuilt immediately to strengthened design). In 989 there was a "great quake" that collapsed some supporting arches, though the domes survived. This time, the repairs took six years to complete. It held up until 1346, when there was another major quake and another partial collapse. This time repairs took 8 years, but they finally got it right, since it has held up well for the last 666 years. Nevertheless, I walked as lightly as possible when I entered.

The history of big domes shows decisively that taller is better. Stable proportions were developed by the Masonic Order that built the great cathedrals of Europe, with buttresses to push inward against the outward push of domes. Very few of the Masonic cathedrals ever collapsed completely, and then only when they were building too high and too slender.

The final development of the dome is in Barcelona, in the Church of the Sagrada Familia, designed by Antonio Gaudi in the 20th century. He finally solved the butress problem completely
Ablution outside the Sultanahmet mosqueAblution outside the Sultanahmet mosqueAblution outside the Sultanahmet mosque

Wash your feet before entering the mosque!
by using a very tall and thin inverted catenary as the shape of the dome.

The catenary is the shape of a chain hanging under gravity. If it hangs long and slender, the force exerted by the chain's supports is pure upward. Invert it and make it into a dome, and the force that the dome exerts on the ground is therefore pure downward. So it is completely stable without any butressing, but it cannot span a wide space. So Gaudi covered the church with a large number of these dome-towers. You probably know what it looks like, but I throw in a photo of the Sagrada Familia just to remind you. Note all the holes in the dome-towers that lighten them.

The Hagia Sophia is so immense that you feel like an insignificant bug when you are inside it. Perhaps that was the point. It was the main cathedral of the Byzantine Emperors, and later the main mosque of the Ottoman Sultans. It was filled with Christain mosaics when Mehmed II took it over. To his credit, he did not destroy them. Some were hidden by plaster, others by huge circular shields with
Sultan's chain, Blue MosqueSultan's chain, Blue MosqueSultan's chain, Blue Mosque

Only the Sultan was allowed to enter on horseback. This chain reminded him to bow his had as he entered.
Arabic holy names on them. In 1935 Attaturk deconsecrated it and it became a museum. Everything was removed; it is now as bare as Topkapi, and it is forbidden by law to utter any prayers to any god inside the place. Two small Christian mosaics outside the main space have been uncovered so you can see them. But if you go there, you go to see the Byzantine architecture, not these two minor mosaics.

It is both dim and bright inside (low hanging chandeliers), and my photos did not come out well. Much better that you click here and look at the professional panoramic photos on the web. On the first page, scroll down until you see a long line of tabs: Mosque, Tomb Palace, Museum, etc. Click on Museum, then click on Hagia Sophia, and you will be in a place with more than 20 panoramic views of the interior. Here you can see much more than you do on a brief tour visit.

We then marched on to the SultanAhmet mosque (the "Blue Mosque"), just a little beyond the Hagia. It was built between 1609 to 1616 by Sultan Ahmet I, who succeded to the throne in 1603 at age 13. The first architect he appointed proposed a small, modest mosque and was immediately strangled right there in the throne room. His successor, Sedefkar Mehmet Agha, proposed instead the most glorious building that the empire could support, and that is what we have today. Like Peter the Great, Ahmet learned a little bit of masonry, and would go over and work personally just to keep up the team's spirit and speed the work along. He was just a teen-age boy at the time.

It is a working mosque, and you might think you would have to take off your shoes, and women would have to wear a scarf. But no, the number of tourists is just too great, so you just put a flimsy plastic sack over your shoes, and women can forget about the scarf. This is weird; the only mosque in Islam to go by these rules. Again, it was dim-bright inside and my pictures are not worth showing. Just click on "Blue Mosque" on the front page of the "Sites in 3D" website. It is a fabulously beautiful interior. Even people who saw it in real life may agree that this web site is better, because they lit the interiors much better than usual.

As you might expect, Agha was a cautious man. The central dome is rather small, but it is surrounded by four half domes that together roof over a space that looks as big as the Hagia. The load is borne by four gigantic "elephant foot" columns on the outer circumference of the central dome, supporting both it and the half domes. They look incapable of collapse; and in fact, nothing here has ever collapsed. Good work, Agha.

Just to prove I was there, I attach photos of a man washing his feet before entering, and a strange iron chain in the gateway to the courtyard outside the mosque.

We saw the site of the Byzantine hippodrome, once famous for its chariot races, then went on to the Grand Bazaar. But I will stop here. It was quite a day.


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