That dude Justinian.

Justinian's wife, Theodora, was a former (ahem) "professional." He himself began a construction spree, and he tightened his grip over all people and did away with all of Constantinople's loved policies. At the Hippodrome, one of the biggest arenas ever, chariot races and other sports took place. He slew all of an army of rebels there at the Hippodrome when they rose against him. After these riots, he sped to rebuild the city to make it grander and more devoted to God. One of his main accomplishments was the building of the Hagia Sophia. This magnificent building was a huge church that was later converted into a mosque. The church has the largest dome ever built at the top. In the end, all of Justinian's military campaigns and his constant building sprees bankrupted the Byzantine Empire.

Here is an aerial view of the Hagia Sophia