The ruins of the 14th-century Olsztyn castle are one of the biggest attractions of the area. The castle, located on a hill, among limestone rocks, is part of the Trail of the Eagles' Nests. It belonged to a system of fortifications, built by King Kazimierz Wielki, to protect western Lesser Poland from Czechs, to whom Silesia belonged at that time. For some time, as a fee, it belonged to Prince Wladyslaw Opolczyk. Taken away from him in 1396, the castle was then handed by King Wladyslaw Jagello to a local nobleman, Jan Odrowąż of Szczekociny. The castle was invaded several times by Silesian princes in the 15th century, and with the advancement of warfare, its fortifications became obsolete. In 1655, it was captured by the Swedes, and since then, it became a ruin. In 1722, it was partly demolished, with bricks used to build a parish church at Olsztyn. Currently, only fragments of defensive walls remain. The most impressive still standing part of the castle is a 35-meter round tower, built in the 13th century, which served as a prison.
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.