Helm's Deep

In J. R. R. Tolkien's Middle-earth high fantasy writings, Helm's Deep was a large valley in the north-western Ered Nimrais (White Mountains).

The valley was described as being blocked over its entire width by the natural series of hills called Helm's Dike and behind that lay the fortress of Aglarond or the Hornburg, at the entrance to the Glittering Caves.

In the Appendices of Lord of the Rings, the history of the valley states that it was home to a small Gondorian regiment, but after the place which was called Calenardhon became Rohan, it became an encampment of the Rohirrim, where the guards of the Fords of Isen lived.

It also states that during the war with the Dunlendings under Wulf, the Rohirrim under King Helm Hammerhand and many of his people sought refuge in the keep, where they held out during the winter of T.A. 2758–2759.

The castle itself was described as having a long causeway which wound up to the great gate of the fortress itself. Inside the keep there were stables and an armoury, as well as a great hall in the rear which was dug out of the mountainside. There also was a great tower (the Hornburg) the top of which consisted of the great horn of Helm Hammerhand. The Deep, which was described as standing next to the fortress, was barred by the long Deeping Wall, which was described as consisting of solid rock except for a small culvert which allowed water from the Deeping Stream to enter; this rendered a fresh supply in sieges of great length. The Deeping Wall itself is described as standing 20 feet tall; and also being wide enough for four men to stand side by side. Access to the fortress from within the Deep was made possible by a long stair which led to the Hornburg's rear gate.

In The Two Towers, the fortress guarding Helm's Deep becomes the refuge of some of the Rohirrim, under King Théoden, and the Battle of the Hornburg was fought there. Théoden said that "Helm's Deep would never fall while men defended it," giving an impression of invulnerability. This is then overturned, as an army Uruk-hai sent by Saruman later almost overwhelm the defences of the Rohirrim. This was achieved by the orcs using an explosive blast of fire within the culvert which, when detonated, destroyed the main defences. The origin of this explosion is unclear and Tolkien denotes it as "Saruman's devilry."