The area around Schloss Seggau has been settled since at least the Roman era,
as demonstrated by the impressive lapidarium which has survived from that pe-
riod. The upper castle was built by the Archbishopric of Salzburg in the twelfth
century as a base for missions and supervision and this original structure was
expanded in 1218 by the bishops of Seckau. Over time, a total of three castles
were built: Burg Leibnitz (belonging to the Archbishopric of Salzburg), the castle
of the bishops of Seckau, and Schloss Polheim. The castles were completed in
their present form under Bishop Johann Ernst, Count of Thun, in the latter half
of the seventeenth century. Schloss Seggau was the residence of the bishops un-
til 1786, after which it remained their summer residence until into the 20th century.