Deeping Wall

From Tolkien Gateway

The Deeping Wall was the solid stone wall, some twenty feet in height and thick enough that four men could walk abreast along the top, 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.[1] In the Battle of the Hornburg (on 3 March, T.A. 3019[2]) 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.[1]