Walls of Constantinople
As the city expanded, new walls were built by the Emperor Theodosius II in the early 5th century about two kilometers west of the original Constantinian walls. The walls consisted of both an inner and outer wall, both made of limestone blocks. The inner wall was at least 5 meters thick and 12 meters high, while the outer wall was at least 2 meters wide and 8-9 meters high.
Over time both sets of walls were significantly damaged by earthquakes and floods and after the Latin conquest at the start of the 13th century, fell into a bad state of disrepair. Nonetheless, the walls remained intact through most of the Ottoman Period, but as the city outgrew its boundaries in the 19th century, sections began to be dismantled. A restoration project financed by UNESCO began in the 1980s, but today the walls are considered one of the most 100 endangered sites in the world.
If you’d prefer to just see a section of the walls, take the tram to the Pazartekke stop, which will place you in the old Topkapi neighborhood of Istanbul and near the gate known as the Topkapi Gate.