Bjørnkær is a 14th century castle mound consisting of two square castle embankments surrounded by a moat and an outer embankment. During excavations in the 1930s, the foundations of a small building were found on the eastern castle embankment. Inside, the building measures about 4.5 m x 6.5 m, and the remains of the entrance door can be seen in the west wall. The other walls have traces of windows. The remains of cobblestones were found outside the building. Bjørnkær was owned by nobleman Niels Kalf. His widow, Abel Puder, gave the castle to the Bishop of Århus in 1427.
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.