Carchost and its counterpart Narchost are the two towers situated on either side of the Black Gate of Mordor (otherwise know as the Morannon) as part of the The Lord of the Rings fictional trilogy. Together, Carchost and Narchost were known as the Towers of the Teeth or even the Teeth of Mordor. They were originally made by the men of Gondor but in the later Third Age they had been long abandoned by the Gondorians and were overrun with evil. Sauron used them as watch towers to guard the dark and evil land of Mordor, protecting it from the very nation which had orginally built them.
Carchost appears to have stood to the eastern side of the Morannon, though specific details of the arrangement of the Towers are hard to come by. The name Carchost contains two Sindarin elements: carch, meaning 'tooth, fang', and ost meaning 'fortress'.