The Asseburg is a ruined hill castle on the narrow, southern crest of the Asse ridge in the Harz Mountains of Germany, not far from Wolfenbüttel.

Based on its dimensions, this elongated fortification was the largest hill castle in North Germany and was considered impregnable.

Burchard was able to withstand during three years, however in 1258 had to relinquish the castle to Duke Albert I. Burchard was then allowed to retreat to Westphalia with his knights, and received a compensation of 400 gold mark for the castle.

After Gunzelin's death in 1260, his sons also lost the county of Peine to the bishop of Hildesheim.

In 1330 the dukes had to pledge the castle to the city of Brunswick, which was interested in securing the trade routes below.