The Fissure is one of two natural boundaries that separate Mountains of Rain and Night from the outside world, the other being the mountains around Three Step Pass. The Fissure is large split in the earth that runs out into the sea, separating the Mountains of Rain and Night from Celtica.
During Morgarath's invasion of Celtica during the Second Araluan Civil War in The Burning Bridge, he constructed a bridge that would carry a large number of Wargals across the Fissure. These Wargals would sweep around to attack King Duncan's army on the Plain of Uthal, coordinating with a frontal assault through Three Step Pass and a number of Skandians attacking through the Fens. However, Will, Horace, and Evanlyn managed to burn this bridge, eliminating the threat, and the Skandians were eliminated by Halt, Gilan and a dispatch of Araluan soldiers, allowing the royal army to push the Wargals back to the Pass, where Horace killed Morgarath in single combat, ending the war and forcing the Wargals to flee into the mountains.