Enrique el León
In 1144 Bursfelde Abbey passed to the control of Henry the Lion, Duke of Saxony (1139) and later also of Bavaria (1156), following the death of Siegfried IV, a grandson of Otto of Nordheim who had died without male issue. Henry the Lion confirmed the rights of the Abbey, following the presentation of a falsified foundation record. The absence of male heirs in the meant that the County of Northeim, including Bursfelde Abbey, now passed to the Guelfs. Henry the Lion reduced his rights over the abbey to rights of patronage and jurisdiction.