In the Elm limestone was mined in medieval times; limestone from the region was used for the tomb of Henry the Lion as well as for the imperial cathedral of Königslutter. In the Middle Ages Königslutter was among the most wealthy cities of the Holy Roman Empire. In 1576 the University of Helmstedt was founded, which was the largest university of protestant Germany. The Duchy of Brunswick (deriving from Brunswick-Lüneburg) created administrative districts (Kreise) in 1833; the District of Helmstedt was one of those districts. It was subdivided into the Ämter of Calvörde, Königslutter, Helmstedt, Schöningen, and Vorsfelde. In 1944, the Amt of Calvörde, which formed an exclave, was moved to the District of Haldensleben, Province of Saxony. During the administrative reforms of the 1970s, northern areas of the district were moved to the District of Gifhorn and to the City of Wolfsburg; the district gained areas in the west from the District of Gifhorn and the District of Brunswick (see List of territorial changes to the District of Helmstedt). During the 20th century, the area between Helmstedt and Schöningen was used for lignite mining by the Braunschweigische Kohlenbergwerke AG. Several villages (Alversdorf, Büddenstedt and Runstedt) were destroyed by surface mining; their inhabitants moved to Helmstedt, Schöningen and to the newly built village of Neu Büddenstedt, later on renamed Büddenstedt.