As the largest and richest city in Europe, many invaders besieged Constantinople over the centuries in hopes of plundering her treasures. A large reason for Constantinople's success as a city were her walls, which are consider among the finest fortifications ever built. The city was a fortress protected by 13 miles of walls, watchtowers, and 50 fortified gates. The primary wall was 40 feet tall and 15 feet thick, with 60 foot towers every 50 yards. In addition there was a 20 foot tall outer wall fronted by a 60 foot wide moat. Though attacked by Goths, Persians, Avars, Arabs, Russians, Bulgars, Normans, Franks, Venetians, and Serbs, in the 1,500 years before 1453, only one attacker, the Fourth Crusade in 1204, successfully entered the city.
Please watch the following short video (4 minutes) for more on the defenses of Constantinople and their importance in history.
The Walls of Constantinople