Although it's a bit of a schlep on the suburban train to get out to Yedikule, this commanding fortress is well worth it. Built in the 5th century by the Emperor Theodosius II, the fortress made up the southern section of Constantinople's defensive walls.
The mammoth arch (blocked up in the late Byzantine period) was known as Porta Aurea (Golden Gate), with doors plated in gold. When the Ottomans conquered the city, they used the fortress for defense, and later as a prison and execution place.
