Thangorodrim - the Mountains of Tyranny - were the three peaks raised above the Gates of Angband by Morgoth after the theft of the Silmarils.

The peaks were made of the slag and ash brought to the surface by the delving of the fortress of Angband. Dark smoke hung about them, and they were a landmark for miles around - an ever-present reminder to the Noldor of the menace in the North.

Thangorodrim was destroyed in the War of Wrath.
Encyclopedia entry originally written by atalante_star