Today, all that remains of the Ardencaple Castle is a tower, perched on the edge of a plateau, looking down on a flat tract of land between it and the shore of the Firth of Clyde. The original castle was thought to have been built sometime in the 12th century, and part of the remains of the original castle were said to have existed in the 19th century. In 1957 most of the castle was demolished by the government in order to build naval housing for the nearby HMNB Clyde (Faslane Naval Base). Today, that sole remaining tower is used as a navigational aid for shipping on the Firth of Clyde. Because of its use as a lighthouse the tower has been called Ardencaple Castle Light.
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.