Basilica of Hagia Sophia.
The construction of Basilica of the Divine Wisdom or Hagia Sofia was carried out in accordance with the order of Emperor Justinian in the VI century. This decision was made after the previous church, which once had stood there, was destroyed during a rebellion. Allegedly, Justinian was the one who said the famous words during the official opening of the basilica, "I surpassed you, Solomon!". Initially, Hagia Sophia was an Orthodox church. However, later it was used as a mosque. Approximately 20 years after the completion of all the construction works, the dome of the basilica was ruined in 558 due to wrong calculations of the project. The pay for this error was very costly – the architects were beheaded.
The current dome was installed in 563. This is a true piece of an architectural art - the perimeter of the building has windows, so it looks like the dome stands on air. Over 900 years Hagia Sophia was the main cathedral of Constantinople (the former name of Istanbul). In 1453, by order of Sultan Mehmet the Conqueror, the Orthodox basilica was converted into a mosque. Several minarets were attached to the building, and the mosaic featuring Byzantine saints was concealed under a thick layer of plaster. Because of this the mosaic has survived till our days.