Thangorodrim.

The three tallest towers of Endor. Infront of Angband raised Morgoth, upon Ard-Galen, after the return from his captivity in Aman in V.Y.t.1495 Thangorodrim. They were built by slag from the furnace and the rubble of the redelwing of Angband and the highest peak was thousend feet above the plain below. At the Main Gate was battlements and at the East and Western side near the edge of Ered Engrin was secret gates. Maedhros was nailed to a cliff upon Thangorodrim and far above the main gate was the terrace where Hurin was imprisoned.

Thangorodrim was crushed in the War of Wrath when Earendil slew Ancalagon and he fell from the sky upon it.

Related Links.: Battles.: War of Wrath.