Valangin castle was a residence of the local lords from mid-12th century to 1566. The oldest visible remains date from the 13th century. It consists of a courtyard surrounded by a rampart and a 'donjon' (keep), which hosts the current museum.
Since 1430 the castle was altered with semicircular towers to be defended against the firearms. The castle was damaged by fire in 1747 which destroyed a whole wing. The dungeon was restored and partly rebuilt between 1769 and 1772. Today Valangin castle is a museum.
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.