The site of the villa Amelungsborn to the west of the present Stadtoldendorf was originally part of the ancestral lands of the Counts of Northeim. Siegfried IV, the last Count of Northeim-Boyneburg and Homburg gave the land at Amelungsborn for the foundation of a Cistercian monastery, which was officially settled by a community of monks from Altenkamp Abbey on 20 November 1135. The abbey was dedicated in 1135 by Bernhard I, Bishop of Hildesheim. The first abbot of Amelungsborn, appointed in 1141, was Heinrich I, a half-brother of the founder, Count Siegfried IV.