The Castle of Charles V is located in the strategic area of Hondarribia, at its highest point. It still conserves the structure of a medieval fortress and its defensive appearance. It was built in the 10th century by King Sancho Abarca of Navarre, although it was subsequently reformed by Emperor Charles V. The building served as both a castle and a palace, both connected by an interior courtyard. The castle had a square floor plan with sturdy walls. Highlights of the main facade include the doorway, rather small in size and decorated with an arch framed by the characteristic Islamic moulding known as an alfiz, over which can be seen the imperial coat of arms with the two-headed eagle of Charles V. It has today been restored and converted into a Parador hotel.
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.