Alburquerque was conquered from Moors by Ferdinand II of León in 1166. It changed hands couple of times before was finally in the hands of Christians in 1217. The castle was built in the late 13th century.
In the mid-15th century Álvaro de Luna, Master of the Order of St. James, built the famous keep. But that is not the only identifying mark on this castle as it has several palace-style out buildings, some outer defence resources in the barbican and a curious pentagonal tower, crowned battlements with sharp points ending in balls. Furthermore, the fortress is protected by three levels of walls scattered with small towers and several doors.
In the early 18th century the city was in the hands of Portuguese and several Vauban-style bastions were added to the complex.
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.