Aglarond e [[Angrenost]] (máis tarde coñecida como [[Isengarda]]) eran as dúas fortalezas construídas por [[Gondor]] para defender os [[Vaos Isen]]. Ao igual que Angrenost ao norte, ao primeiro estivo ben custodiada, mais a medida que a poboación de [[Calenardhon]] (que despois sería o reino de [[Rohan]])
foi diminuíndo, foise abandonando e perdendo importancia, até acabr nas mans dun pequeno corpo de garda que se mesturou cos [[Dunlending]]s.
Cando [[Cirion]], [[Mordomo de Gondor]], outorgou Calenardhon a [[Éothéod]], Aglarond pasou aos coidados dos [[Rohirrim]], que a chamaron '''Súthburg''' (burgo do sur no seu idioma).
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]].
After the war, [[Gimli (Middle-earth)|Gimli]] the [[Dwarf (Middle-earth)|Dwarf]], who fought in that battle, established a colony of [[Durin's folk]] there. Aglarond lay in front of a huge and very beautiful cave system, which proved irresistible to him. Gimli became known as 'the Lord of the Glittering Caves', although this new realm was presumably under the overlordship of [[List of Middle-earth Dwarves#Thorin III Stonehelm|Thorin Stonehelm]], his kinsman and heir of the lordship of all Durin's Folk. The dwarves of Aglarond restored the Hornburg following the War of the Ring, and it became a fortress they shared with the [[Rohirrim]].