Mainz Citadel

The Mainz Citadel is located on the Jakobsberg on the edge of today's old town and in the immediate vicinity of the Roman Theater train station. The fortress was built in its current form around 1660 and was part of the Mainz fortress. de.wikipedia.org/wiki/Zitadelle_Mainz
zitadelle-mainz.de

In the 1960s, the citadel housed the commercial vocational school of the city of Mainz until it moved to the new building on the Hartenberg. Today the citadel belongs to the city of Mainz and houses numerous municipal offices.

Definition citadel ("small town"): A citadel is a small self-contained fortress that either lies within a larger fortress or forms part of the enceinte (i.e. the main line of fortifications) of the larger fortress. When the city was stormed by enemy troops, it served as a retreat for the garrison and the city's last core of resistance.The citadel and its surroundings document the history of Mainz in a small space: starting with the Roman Drususstein memorial and the barracks built during the federal fortifications in the 19th century to the air raid shelters of the Second World War.
In October 2015, the Mainz citadel received the Hague Plaque from UNESCO, which marks the building as protected.