Gmünd Castle dates from the mid-13th century. During the Austrian-Hungarian War in 1487 it was occupied and destroyed by the troops of King Matthias Corvinus after a seven-years-long siege, and rebuilt from 1502 to 1506 under the Salzburg archbishop Leonhard von Keutschach. During the German Peasants' War of 1525, it was again besieged, though not captured. Archbishop Wolf Dietrich Raitenau had the building enlarged in 1607. Devastated by a fire in 1886, it was restored from 1950 and is today used for theatrical performances, concerts and lectures, including a viewing tower and a restaurant.
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.