Carchost

One of the two tall towers that stood on either side of the Morannon, the Black Gate of Mordor, that were together known as the Towers of the Teeth or the Teeth of Mordor. Carchost and its companion Narchost were originally the work of the Men of Gondor, but by the later Third Age both the towers had long been abandoned by the Gondorians. When Sauron returned to his Black Land, he repaired and rearmed Carhost and Narchost, so that they came to guard his borders against the very nation that had originally built them.