The first mention of Graville Abbey was in the 9th century. Considered to be a masterpiece of the Romanesque art in Normandy, the abbey underwent several periods of construction since the 11th century. The church's nave and transept date from the Romanesque period. Guillaume Malet de Graville, who was victorious during the Hastings battle alongside William the Conqueror, as well as his descendants, invested their fortune in preserving the riches of this monument. Today conventual buildings are converted to a museum.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.