Fort Nieulay, located along the Avenue Pierre Coubertin, was originally dated to the 12th or 13th century. During the English invasion in 1346, sluices gates were added as water defences and a fort was built up around it in 1525 on the principle that the people of the fort could defend the town by flooding it. In April and May 1677, Louis XIV and Vauban visited Calais and ordered a complete rebuilding of Fort Nieulay. It was completed in 1679, with the purpose to protect the bridge of Nieulay crossing the Hames River. By 1815 the fort had fallen into a ruined state and it wasn't until 1903 that it was sold and improved by its farmer tenants. The fort was briefly the site of a low-key scuffle with Germans in May 1940.
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.