Asserbo Castle was founded by Bishop Absalon in the 1100s as a monastery for monks of the Carthusian Order. The castle was taken over first by the King around 1560 and in subsequent centuries by drifting sand. The castle was liberated from the sand in two phases: initially by King Frederik VII in 1849 and then by National Museum excavations in 1972.
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.