From 1253 to 1719, the prince-bishops resided in Marienberg fortress, built on a commanding height over the west bank of the Main. The medieval castle was transformed into a Renaissance palace c 1600. The Furstenbaumuseum comprises the bishops' apartments, richly furnished and hung with paintings and tapestries, including some from religious edifices. A splendid 13C circular keep, a Renaissance covered well and a circular chapel devoted to the Virgin Mary grace the central rectangular courtyard.