Checkpoint Charlie (or 'Checkpoint C') was the name given by the Western Allies to the best-known Berlin Wall crossing point between East Berlin and West Berlin during the Cold War.
GDR leader Walter Ulbricht agitated and maneuvered to get the Soviet Union's permission for the construction of the Berlin Wall in 1961 to stop Eastern Bloc emigration westward through the Soviet border system, preventing escape across the city sector border from East Berlin to West Berlin. Checkpoint Charlie became a symbol of the Cold War, representing the separation of East and West. Soviet and American tanks briefly faced each other at the location during the Berlin Crisis of 1961.
After the dissolution of the Eastern Bloc and the reunification of Germany, the building at Checkpoint Charlie became a tourist attraction. It is now located in the Allied Museum in the Dahlem neighborhood of Berlin.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.