Known as “the Mother Church” by Byzantine Chrisitians, the Church of Hagia Sophia (Holy Wisdom), stood for 900 years as the center of the Empire and of Eastern Christianity.

The Emperor Justinian knew he was building a church for all time. He nearly bankrupted Constantinople to build it. The city watched one fountain after another dry up — all the pipes had been melted down to make gutters for the new church. The teachers in the schools were starving. The poor were poorer, and the rich complained of being somewhat less rich. But the church was going up, and for a while Justinian hardly seemed to care about anything else.

His architect, Anthemius, was a brilliant but slightly eccentric engineer. Anthemius invented a kind of searchlight, and he used it to play practical jokes on his neighbors. He also invented a steam engine, but it was only a mechanical toy. Anthemius was just the sort of mildly unbalanced architect who would try something just because it was supposed to be impossible, and just the sort to build the most magnificent church in the world — or die trying.

The impossible problem was this: how do you give a building both light and space? The bigger the building, the heavier the roof. The heavier the roof, the thicker the supports it needs, and the less space there is for letting in light.

Anthemius’ answer was a huge, shallow dome. It ought to have been impossible. Nothing like it had ever been done before — a big dome usually has to be tall, like the dome of St. Peter’s in Rome or the Capitol in Washington, in order to hold itself up. Even if the dome could be built, the supports for it would have to be so thick that they would ruin the effect of light and space.

But nothing seemed impossible for Anthemius. He solved the problem by setting the dome on half-domes, so that the whole structure could rest on four widely spaced piers. Around the circumference of the dome were so many windows that the dome seemed to float over the church. Provincial visitors sometimes believed the story that the dome hung from heaven on a golden chain.

Anthemius had solved the impossible problem—at least so it seemed. When Justinian finally entered the finished church, he looked up at a mosaic picture of Solomon. “Glory to God,” said the Emperor, “who has found me worthy to finish such a great work — surpassing even you, Solomon.”

A few years later, the impossible dome fell down.

Even making the dome slightly taller didn’t solve the structural problems. But the dome was too beautiful to give up on. When it was rebuilt for the last time, the builders took no chances. Exceptionally holy men came to spit some of their holiness into the mortar. A saint’s relic was built into every twelfth course of bricks. And every brick was stamped with the initials of the verse, “God is in the midst of her; she shall not be moved.”

With all that supernatural help, the dome stayed up. Earthquakes, sieges, and periods of neglect have taken their toll on the building, but with the help of occasional emergency repairs, the dome is still there today — though the building the Turks call “Aya Sofia” is now a state-run museum. The last liturgy was offered there in 1453. Afterward, the building was converted to a mosque.

The Orthodox Patriarchate of Constantinople hosts a lovely website of high-quality photos of the Mother Church. Don’t miss it.