Istanbul is known as Constantinople, which in turn was the former Byzantium. The city is rich in history. It was really rich too, as it had been the capital city of the empires for more than a thousand years. The most amazing historical building among the many must be this one, Hagia Sophia. This was constructed as a church and then turned into a mosque, and now a museum. It is unbelievably big inside. Can't imagine that they built such mega building 1500 years ago.
伊斯坦布尔 三朝帝都
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From @sunray