The site of Andechs was originally occupied by a castle belonging to the counts of Dießen on the Ammersee, probably built on a Roman castra, and remained the seat of the powerful counts of Dießen-Andechs (1135 to 1180) and dukes of Andechs-Meranien (1180 to 1248). In 1132 the count donated his ancestral seat at Dießen to the Holy See and removed to Andechs.