The Citadel is one of the largest and best-preserved town fortresses in Europe.
It is also known by its French name, Citadelle Petersberg, as French troops were stationed there from 1806 to 1814, when Erfurt was under Napoleonic occupation.
Napoleon visited Erfurt several times and the citadel was further developed during his rule, although parts of it were damaged in a battle in 1813.(source: Wikipedia)