The Towers of the Teeth were two towers that stood on two sheer hills that were thrust forward on either side of the mouth of the pass of Cirith Gorgor at the northwestern end of Mordor where the Ered Lithui met the Ephel Duath. They were strong, tall, stony-faced and had dark window-holes facing north, east and west. The tower on the western side of the pass was called Narchost and the tower on the eastern side of the pass was called Carchost.
In S.A. 3434, the Battle of Dagorlad took place at the plain Dagorlad in front of the Black Gate.
After the defeat of Sauron in the War of the Last Alliance the Men of Gondor built the Towers of the Teeth to prevent Sauron from returning to Mordor and to keep watch on Mordor where the creatures of Sauron still lurked.
After the Great Plague devastated Gondor in T.A. 1636, the watch on the borders of Mordor ceased and the fortresses that guarded the passes were unmanned in T.A. 1640 because of a lack of troops. It is possible that the Towers of the Teeth and the other fortresses that guarded the passes into Mordor were only abandoned temporarily and were manned again by troops from Gondor when sufficient troops became available again later.
At the time of the death of king Ondoher the Towers of the Teeth were still manned by the Men of Gondor.
As the strength of Gondor failed, the Towers of the Teeth were abandoned by the Men of Gondor and were empty for long years and fell into decay. After the return of Sauron they were repaired and garrisoned with the forces of Sauron. The Towers of the Teeth fell down during an earthquake after an eruption of Orodruin when the One Ring fell into the Sammath Naur in the Orodruin on 25 March T.A. 3019.