The Citadel Namur is a fortress dates originally from the Roman era, but has been rebuilt several times. Its current form was designed by Menno van Coehoorn, and improved upon by Vauban after the siege of 1692. It has been classified as a Wallonia's Major Heritage site.
The original citadel dates to 937. It achieved its present extent between 1631 and 1675, when the city was under Dutch control. This section was called Terra Nova to distinguish it from the smaller fort built adjacent in 1542 and ensuing years. A variety of subsidiary positions were built in the 18th century. It was disestablished as a military post in 1891, superseded by a new ring of forts around Namur that were calculated to prevent the city from being attacked with artillery. This ring became the Fortified Position of Namur in the 1930s.
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.