Basilica Cistern and Hippodrome of Istanbul

The Basilica Cistern was constructed by Justinian I around 524.
It is 70m in width and 140 m in length, with a dome
covering an area of 9800 square meters.
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The Hippodrome was a Byzantine stadium with seating for 100,000
spectators, and was the center for public entertainment such as
chariot races and circuses. Two columns and an obelisk still stand.