and [[Angrenost]] ( later [[ Isengard]]) were the two fortresses built by [[Gondor]] guarding the [[ Fords of Isen]]. Like Angrenost to the north it was initially well guarded, but as the population of [[Calenardhon]] ( the later [[Rohan]]) dwindled it was not maintained and, losing importance, was left to a hereditary small guard who intermarried with [[Dunlending]]s.
When [[Cirion]], [[ Steward of Gondor]], gave Calenardhon to the [[Éothéod]], Aglarond was transferred into [[Rohirrim |Rohirric]] care, who named it '''Súthburg''' ( southern burg in their language). The Gondorian guard was merged with that of [[Angrenost]] to the north, which remained in the keep of Gondor. Guard duty of the Fords was initially shared between Gondor and Rohan, but later maintained only by the Rohirrim.
During the reign of [[Helm Hammerhand]], [[Rohan]] was attacked by Dunlendings from across the river [[Isen (Middle-earth)|Isen]]. [[Edoras]] was taken, and Helm and many of his people retreated to Súthburg. Because Helm always blew a great horn before riding out to fight the beleaguering [[Dunlendings]], the keep was renamed '''Hornburg'''. During the [[War of the Ring]], the Hornburg was the refuge of the [[Rohirrim]] as they defended [[Battle of the Hornburg|Helm's Deep]].