The Alcázar of Seville is a royal palace, built for the Christian king Peter of Castile. It was built by Castilian Christians on the site of an Abbadid Muslim residential fortress destroyed after the Christian conquest of Seville. The palace, a pre-eminent example of Mudéjar architecture in the Iberian Peninsula, is renowned as one of the most beautiful. The upper levels of the Alcázar are still used by the royal family as their official residence in Seville, and are administered by the Patrimonio Nacional. It was registered in 1987 by UNESCO as a World Heritage Site.
The original nucleus of the Alcázar was constructed in the 10th century as the palace of the Muslim governor. Built and rebuilt from the early Middle Ages right up to our times, it consists of a group of palatial buildings and extensive gardens. The Alcázar embraces a rare compendium of cultures where areas of the original Almohad palace - such as the 'Patio del Yeso' or the 'Jardines del Crucero' - coexist with the Palacio de Pedro I representing Spanish Mudejar art, together with other constructions displaying every cultural style from the Renaissance to the Neoclassical.
Some gardens have Renaissance statues. After damage by the 1755 Lisbon earthquake, that façade of the Palacio Gótico overlooking the Patio del Crucero was completely renovated in Baroque style.
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.