Hagia Sophia in Istanbul is a beautiful and extraordinary example of surviving Byzantine architecture. The original Hagia Sophia was built in the fourth century by Constantine the Great, the first Christian emperor and the founder of Constantinople. Hagia Sophia was one of several churches he built in important cities throughout his empire.
The church was destroyed and rebuilt several times in the fourth century. It was rebuilt in its present form between 532 and 537. Since then the dome has collapsed several times and the church has been attacked by crusaders.
In 1453 Sultan Mehmet the Conqueror commenced the siege of Constantinople with an army between 80.000 and 200.000 troops and a navy of 320 vessels. This brought and end to the Eastern Roman Empire. Mehmet was amazed at the beauty of Hagia Sophia and immediately converted it into his imperial mosque. It became a model for many later mosques in Istanbul.
In 1934 the Turkish president Kemal Atatürk turned the mosque into a museum. It's still a museum and open for the public to visit.