The Fortress Marienberg lies 100 m above the river Main. For nearly five centuries the Marienfeste was the palace of the prince-bishop of Würzburg. The first fortress on the site was a Celtic refuge castle (ca. 1000 BC). A medieval fortress was built here. In 1631, during the Thirty Years' War the fortress was taken by the Swedish king Gustav Adolf. After the year 1642 the fortress was rebuilt. The palace was remodelled in Baroque style. Two rings of heavy fortifications were added. The Baroque garden of the prince-bishop faces the city of Würzburg. This place used to be a canon emplacement. The canons were actually facing the city! Thus the prince-bishop wanted to remind the citizens of Würzburg of his power.