Leonhard's Church was a small Romanesque hall church. Its main portal resembled the portals of the Peterskirche. It was mentioned by name for the first time as early as 1185 and served as a parish church for the residential houses on the Petersberg slope that stood until the fortress was built. In 1677 it was profaned and from then on used for military purposes as an armory. In the last days of the Second World War, the Leonhard Church was almost completely destroyed.