Alte Burg (Old Castle) was built on the foundations of a round tower dating back to the times of the Roman empire. In the late 13th century the original structure was extended by order of Archbishop Heinrich II von Finstingen. A moated castle was built which became part of the city fortifications. During the centuries that followed Alte Burg has continuously been modified and reconstructed and Renaissance and Baroque style extensions were added. The building has two towers facing the Mosel and a third for the richly ornamented spiral staircase built in 1557. Roofs and cupolas were made ​​by the court architect Johann Christoph Sebastiani, who was also responsible for the reconstruction of the castle of 1680 to 1682. Alte Burg now houses the City Archive and the City Library.