The Castle of Osma is a medieval castle which seems to have been built in the 10th century. It was built in stone, although Count Gonzalo Tello used some Roman structures and materials which belonged to a small Christian fortress.
The castle is divided into three walled enclosures which can be easily distinguished. Nowadays you can see the ruins of this fortress which adapts perfectly to the rocky hill between the Ucero and Abión rivers, near the famous Roman city of Uxama. It was used mainly as a defensive structure located in the natural passageway to this valley and the City of Osma. Some of the walls of the main enclosure are still standing which help to make out the floor plan and you can still see its Keep, remains of other towers, the access gate and a small door. There are also remains of the other two enclosures that improved the castle’s protection. On the outer wall that goes down the hillside, you can see the Water Tower (Torre del Agua) that is located near the river.
The Castle of Osma has experienced many battles from its first reconquest in 912 all the way up to the last in 1088, and in the 15th century, it belonged to the bishop of Osma.
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.