Teutonic Knights conquered the Ełk area in 1283. They built first a wooden castle to the site of former Old Prussian settlement and the town grew around it. It was first documented in 1398. The brick castle was built in 1497. In 1888 the castle was rebuilt - it became a prison and had that function until 1976. In 1958 during renovation of part of ther castle, under its walls, there was a collapsed tunnel found. After 1985 the castle doesn't have nor any function neither conservation care.
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.