In 955, Almería gained the title of medina ('city') by the Caliph of Cordoba, Abd ar-Rahman III: construction of the defensive citadel, located in the upper sector of the city, began in this period. The alcazaba, provided not only with walls and towers but also with squares, houses and a mosque, was to be also the seat of the local government, commanding the city and the sea nearby.
The complex was enlarged under caliph Al-Mansur and, later, under Al-Jairan, first king of the independent taifa of Almería (1012–1028).
The first line of walls is a wide enclosure corresponding to the first Muslim military camp, used as shelter for the population in case of siege. For this task it was provided with large cisterns.
The first enclosure is separated by the second one by the so-called Muro de la Vela ('Wall of the Sail'), taking its name from a bell that warned the population in case of events such as the arrival of a ship in the port, danger, fires etc. This wall was built by King Charles III of Spain.
In the second enclosure was the residence for the governors, their soldiers and their servants. It included also the mosque, baths, tanks, tents etc.
The third enclosure, the most external, is also the most modern in the complex. After the Christian conquest of Almería, the Catholic monarchs Isabella I of Castile and Ferdinand II of Aragon had a castle built in the most elevated sector of the town, more apt to resist the new gunpowder artillery.
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.