Ancalagon breaks Thangorodrim

But Eärendil came, shining with white flame, and about Vingilot were gathered all the great birds of heaven and Thorondor was their captain, and ther was battle in the air all the day and through a dark night of doubt. Before the rising of the sun Eärendil slew Ancalagon the Black, the mightiest of the dragonhost, and cast him from the sky; and he fell upon the towers of Thangorodrim, and they were broken in his ruin.

-The Silmarillion