The defensive wall of Helm's Deep.
"A wall, too, the men of old had made from the Hornburg to the southern cliff, barring the entrance to the gorge."
(The Two Towers III 7, Helm's Deep)
The solid stone wall, some twenty feet in height, that defended the refuges of the Rohirrim at Helm's Deep. It lay beneath the castle of the Hornburg, to which it was connected by a flight of steps. In the Battle of the Hornburg, it was breached for the only time in its history by a besieging army of Orcs and Dunlendings, but they were soon driven back and defeated.