Carach Angren

The pass in the northwest of Mordor, also called by the Mannish name Isenmouthe (both versions of the name mean 'iron jaws'). It was formed where spurs reaching out from the ranges of Ephel Dúath and Ered Lithui met, leaving only a narrow passage between the Plateau of Gorgoroth and the smaller valley of Udûn to the north.

As the inner entrance to Mordor behind the Black Gate of the Morannon, Carach Angren was heavily fortified, and both the rocky spurs that overlooked it carried fortresses and watchtowers. Across the passage itself, a wall of earth had been built, and a great ditch had been dug across the opening, spanned by a single bridge.