Castillo de San Felipe was built in 1771 during the reign of Carlos III of Spain for the defense of the littoral. It was disarmed by the French army during the Spanish Independence War. Halfway into the 19th century it was occupied by the special forces in charge of the surveillance of the littoral. During the 20th century was abandoned and repaired between 1990-1991.
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.