Friday, July 8, 2011

Domes and Squinches

I can’t tell you exactly why I have this deep thing for domes—but I do. It all started back with the Brunelleschi dome in Florence in about 1988 where for a few moments I felt as if the spaciousness of the dome resided in my body. I was just sitting underneath it, breathing, and it happened. It was incredible. So the domes of Iran, every bit as spectacular as those in Florence—maybe even more so—have rekindled this deep love, from the simplest like the ice house in Meybod to the most extraordinary like the one in Imam Mosque in Esfahan.

I’m not going to go into the whole history of domes or we’ll be here for pages. Let’s just say that it’s possible to build a dome onto a round building, like the cistern in Yazd to the left, or an octagonal building, like the 1615 madraseh in Shiraz below, without much trouble—except the building of the dome itself. In those parts of Persia where wood was not available, sun baked bricks and mud were used to make houses with vaults, arches, and domes using a system called corbeling. During the Sassanian Dynasty (224-650), round domed Zoroastrian Fire Temples were often built. You’ll also remember that tombs were often octagonal buildings with domes.

In preparing for the trip three years ago, I read Jason Elliot’s Mirrors of the Unseen and a Robert Byron's Road to Oxiana, both of which made me aware of the awesome and daunting task of putting a round object on top of a square one. A little like a square peg in a round hole but upside down. They introduced me to the squinch. (Sounds like something from A Cat in a Hat, doesn’t it.) The first time I saw one—three years ago in Esfahan—I couldn’t help but run around to everyone in the group saying “Do you know what that is?” Pointing up to a corner… “That’s a squinch.” No one was as excited as I. And it’s probably true to this day.

So here’s the thing about squinches: In order to put a dome on a square building, there needs to be an architectural device that forms a transition between the two. If you just plunked down a dome on top of a square, the dome would be supported only just a little bit on the four sides—and that is not enough support.

A squinch is an arch set at an angle on each corner of the building, turning the square into an octagon, as you can see in the diagram to the left. (Source: Dr. Outahbachi-Imad, Kansas State University) An arch is placed on each side wall extending to the same height as the squinch. As time went along, a row of 16 smaller arches, above the squinches and set over the angles of the octagon, formed a 16-sided polygon, as you can see above in the 15th century Alexander's Prison in Yazd. A polygon is a whole lot closer to a circle than a square, and there are 16 points of connection rather than just eight or four. Now you can safely build the dome on top of it. So there, now you are formally introduced to the squinch.

But what is truly amazing, to me anyway, is that the Persians in the Sassanian Dynasty (224-650) invented them. You can see a good example in the Sarvestan Palace which was built 420-438 by King Bahram V in the middle of an empty plain. Located about 90 kilometers east of Shiraz, the building could have been a palace but it could also have been a fire temple. You can see the very simple squinch to the left. Thanks to the internet for these two great photos.
Jamah Mosque in Esfahan which was built over time starting around 771 has an interesting example of a more highly developed system of squinches. This squinch and north dome, in two photos to the left, were built by the Seljuk ruler Taj al-Mulk in 1088 in competition with his rival Nizam al-Mulk who built a similar, but less impressive, south dome in 1086-87.

There is a lot more I could say about domes, but let me add just this: Domes  can be single shelled (or walled), double shelled or even triple shelled. Having multiple domes lightens and strengthens the structure in ways I don't entirely understand but it has to do with weight and thrust. The first double shelled dome we saw was the Oljeitu Mausoleum at Soltaniyeh, built from 1302-1312 during the Ilkhanid Dynasty.

I found the double shelled of Imam Mosque in Esfahan, completed in 1629, the most interesting because the outer shell is a different shape from the inner one.  As you can see in the photo to the left, the outer one has more of a point and the windows are located in the drum below the dome. On the inside, the dome is much flatter and the windows are located in the dome itself.

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