The walls of Constantinople were the greatest fortifications of the medieval age and, although they were severely damaged by Sultan Mehmet II's canon in the siege leading up to the Ottoman conquest of the city in 1453, large sections still stand more or less intact today. The walls were built in the 5th century after the city outgrew the walls built by Constantine, and they stretched 6½ km (4 miles) from the Marmara Sea to the Golden Horn. The "wall" was actually made up of a large inner and smaller outer wall, with various towers and gates, as well as a moat. Parts have been restored and you can even climb around on top; the easiest section on which to do this is near Edirnekapı, a short walk uphill from Chora Church.
From Edirnekapı, if you walk along the inside of the walls for a few hundred yards north in the direction of the Golden Horn, you will come to what is known in Turkish as the Tekfur Sarayı (Hoca Şakir Cad.), a large three-story building that has an impressive
facade and is built into the city walls. This 13th-century edifice represents the only significant remains of the multibuilding Palace of Blachernae, which served as the Byzantine emperors' primary residence after they recaptured Constantinople from the Latin Crusaders in 1261. The Tekfur Sarayı is supposedly being restored and as of this writing, entrance to the site is prohibited. Much of the walls close to the Golden Horn are also difficult to access due to an ongoing "urban regeneration" project being carried out in the surrounding Ayvansaray neighborhood.