[The following post was reprinted with permission from the blog of architect Dino Marcantonio.]
The Byzantine style, like Gothic, Georgian, and Art Deco, is another wonderful experiment in that great laboratory called the Greco-Roman tradition. Constantine planted the seed when he moved the capital of his empire from Rome to Byzantium. At that time, owing to its history, the tradition in Byzantium would likely have been Greco-Roman with a Persian flair. Constantine set the Greek craftsmen practicing there to work on monumental projects the scale of which they had never seen, and he made New Rome the greatest city in the empire.
The Church of the Holy Apostles, here depicted in an illuminated manuscript, was built by Constantine as a tomb for himself with relics of the twelve apostles. Rebuilt by Justinian, it was the most important church in Christendom after the Hagia Sophia.
Over time the Byzantine style matured as two potent ideas, one architectural and the other theological, led to its two characteristic features. They are the pendentive, and the concern about idolatry.
THE PENDENTIVE
The pendentive was the invention of the brilliant architects and masons of Constantinople who wanted to figure out a way to unite the monumental Roman dome with the traditional basilican plan and cruciform plan. The problem they had was that the only way anyone knew how to support a dome was to set it upon a circular or polygonal plan, as at the Pantheon, for example. For it is impossible to build a dome on top of a cube out of masonry.
Imagine the volume above built out of brick. The bricks defining those flat wedges at each of the corners next to the dome would fall instantly to the ground. So they had to devise a way to mediate between the dome and the cube so that, brick by brick, the forces of gravity would be transferred smoothly down to the ground. Here is how it was done.
Step 1: Start with a hemisphere.
Step 2: Take four slices out of the hemisphere such that each slice meets the next at a point. (This volume is called an umbrella dome.)
Step 3: Slice off the top. Voilà, you are left with a volume which is circular on top, and square on the bottom. The shaded areas are the actual pendentives which are doing all the heavy lifting.
Step 4: Now you can add a hemispherical dome to the top, and a cube on the bottom. Perfect for a church crossing.
Step 5: For added lift, you can add a cylinder, or drum, between the pendentives and the dome.
Thanks to the invention of the pendentive, the Byzantines were able to build the Hagia Sophia and its many offspring. Aside from the symbolic value of the monumental dome, there is also the practical advantage that comes with roofing a building with masonry instead of timber trusses: fire protection. The masons in the region had already developed by this time the ability to build small domes without centering, or temporary supports (this little video will give you an idea how). The monumental dome would have been the natural ambition for them.
Domes were often arrayed in a quincunxial pattern. For the sake of formal coherence with the dome motif, its close relatives the vault and the arch play supporting roles (no pun intended!). Rather than the usual entablature spanning a colonnade then, one finds rows of arches lined up liked camels in a caravan. Horizontal lines in general are muted.
The pendentives of the Hagia Sophia are decorated with Seraphim, the highest of the choirs of angels, with six wings and many eyes (Revelation 4:8). They support the dome of Heaven.
[Image source]
