With the aim of converting the then Sorbian population of the region to Christianity, the Benedictine abbey that had been founded in 970 in Thankmarsfelde in the Harz Mountains was transferred in 975 to the fortress of Nienburg, originally built by order of Charlemagne.

The construction work necessary to convert the building took over 30 years and the newly built abbey church, which is still extant, was eventually dedicated on 8 August 1004 in the presence of Emperor Henry II, who was at the time waging war against the Poles.

It owned many estates and villages (including Harzgerode, Niemitsch and Lübben), but they were isolated and scattered between the Harz and the Lausitzer Neisse, and the last threat against the possessions of Nienburg Abbey from rebellious Sorbs was as late as 1115.

[1] In the second half of the 12th century the abbey was involved in a regional power struggle in which it eventually lost its independence and in 1166 became a possession of the Archbishops of Magdeburg.

As a consequence of the Reformation and the German Peasants' War the abbey was handed over in 1563 to the Princes of Anhalt, who converted the conventual buildings between 1680 and 1690 for use as a castle for the use of their widows.