The castle of San Esteban de Gormaz is one of the key castles that changed ruler once and again during the 10th and 11th century when it finally came under Christian domain. During the reign of King García I, king of Leon, it was reinforced giving place to a repopulation of the town. From there, soldiers would control transit through the Douro River and they would guard the bridge that passed over this river. Nowadays, what is left of the castle is a large wall that is about two metres thick. The castle was built with ashlar stonework, possibly of Roman origin.
Near the access gate, there is a great opening in the ground known as Pozo Lairón, although is not certain what it was used for. The castle is narrow and elongated, and inside there are remains of water pools and underground constructions. Although it is quite deteriorated, it is of great importance due to its strategical location from which you can see the castle of Gormaz.
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.