The construction of the Niebla Castle started in 1402, when Don Enrique de Guzmán, the second Duke of Medinasidonia and the fourth of Niebla, pulled down the old Moorish Alcázar to build the one we know today. The result was a magnificent royal palace which preserved the most interesting and luxurious parts built by the Arabs, such as the Muslim Tower of Homage.
After the works of restoration made in the last few years, the Alcázar is now in good conditions. It has a rectangular structure divided by an inner wall which separates the patio of arms from the luxurious rooms intended as palace. This main structure has ten towers; six of them are square (four are on the corners -including the Tower of Homage - and two of them are at the ends of the inner wall). The other four are semicircular cubes alternated with the square ones. The walls go on from the Tower of Homage and the one located on the north-west angle to form a barbican surrounding the central building on the east, south and west sides. This barbican has six towers and joins the almohade wall near the Puerta de Sevilla and del Socorro. An adarve and a barbican built in the late 15th century completed the building.
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.