Yedikule Fortress in Fatih

You're standing at the Golden Gate, on the edge of old Constantinople, close to the Sea of Marmara. What you're looking at is really two things in one: a Roman triumphal arch and an Ottoman fortress. Start with the two big marble towers. Between them stood the Porta Aurea, the most important of the seven gates in the land walls. It was fifteen metres high and covered in gold plates. There were carved elephants on top, and the towers were decorated with gold and bronze sculptures. Quite an entrance.