Nelig Myrn.

The Teeth-towers. One named Narchost, the other Carchost.

the stem Nél-ek. = Tooth

The two Teeth-towers, Narchost and Carchost, one at each side of Morannon in Ered Lithui and the outer ( Northern ) Cirith Gorgor, were build by the Gondorians upon two black-boned sheer hills to protect the Northern intrance to Mordor. The towers were built by Gondor as a protection against Sauron to prevent his return into Mordor and for keeping the evil that still lurked in Mordor inside. The exact time for there building is not told but it would have had to be no earlier than Second age 3441 where the siege of Barad-Dûr began but it is more likely it was after the overthrow and flight of Sauron. besides the Teeth-Towers Gondor built Durthang and the Tower of Cirith Ungol.

But the strength and pover of Gondor failed and the towers fell into decay and stood empty and Sauron returned, the towers were repaired and filled with servants of Sauron.