The first documents testifying to the existence of a castle in Castro date back to the 13th century: a document of 1282 described it as having a strategic importance to protect the kingdom. It is quite sure that the castle was built on the ruins of a former Byzantine building, which protected the fortified Roman village. In 1480 it was destroyed and then rebuilt and strengthened  in 1572 by the Spanish viceroy.
On the north-western part, stand the thick walls of the Bastion of the buttress, with a single central room and fortified battlements. The Torre Cavaliera, the highest and most imposing one, is a three-story tower with three rooms, covered with barrel vault. The Torre Circolare, dating back to the Aragonese period, has three rooms with small windows and merlons with machicolation.
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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.