Súthburg
From Tolkien Gateway
Súthburg was the name originally given by the Rohirrim to the fortress of Aglarond. This was due to it being the southern of the fortresses that guarded the Gap of Rohan and the Fords of Isen, Isengard being the other. After Helm Hammerhand sought refuge there in T.A. 2759, it was renamed Hornburg.