Monterrei Castle is located a high part of the valley, near the town of Verín. It was built in the 12th century by Alfonso Henríquez. It was extremely important in the epoch of Peter the Cruel. In the 16th century it was used by Philip the Handsome for a meeting with Cardinal Cisneros. It was built from stone with evenly dressed ashlars. The most notable exterior features are the two towers: the Ladies Tower and the Keep The Keep was built by Sancho Sánchez de Ulloa in 1482. The castle is now 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.