The mouth of the gorge, Helm's Gate, was closed by the battlemented Deeping Wall, tall, and wide enough for four men to stand abreast, with a culvert for the Deeping-stream which flowed down the valley. At one end of the wall the Hornburg castle stood on a spur of the mountain; a long stair led to its rear gate, and a long causeway led down forwards from its main gate. About two furlongs (400 metres) down from the gate was an outer trench and rampart, Helm's Dike, built right across the Deeping-coomb. Tolkien drew detailed sketches of the fortifications.