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 Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.