Great engines crawled across the field; and in the midst was a huge ram, great as a forest-tree a hundred feet in length, swinging on mighty chains. Long had it been forging in the dark smithies of Mordor, and its hideous head, founded of black steel, was shaped in the likeness of a ravening wolf; on it spells of ruin lay. Grond they named it, in memory of the Hammer of the Underworld of old. Great beasts drew it, Orcs surrounded it, and behind walked mountain-trolls to wield it.
...
The drums rolled and rattled. With a vast rush Grond was hurled forward by huge hands. It reached the Gate. It swung. A deep boom rumbled through the City like thunder running in the clouds. But the doors of iron and posts of steel withstood the stroke.
Then the Black Captain rose in his stirrups and cried aloud in a dreadful voice, speaking in some forgotten tongue words of power and terror to rend both heart and stone.
Thrice he cried. Thrice the great ram boomed. And suddenly upon the last stroke the Gate of Gondor broke. As if stricken by some blasting spell it burst asunder: there was a flash of searing lightning, and the doors tumbled in riven fragments to the ground.

(LoTR, V-4)

Grond - The battering-ram used against the Gate of Minas Tirith was named after it [The great mace of Morgoth] (The Return of the King V 4). 185

(Silm, Appendix)