Great beast

Great beasts or yurgs were rhinoceros-like creatures of burden in Middle-Earth.

Use in the War of the Ring
The Great Beasts used by Sauron's armies as burden beasts, most notably during the Battle at Minas Tirith. They were used by the Orcs of Mordor to pull the greatest seige weapon, Grond, to knock through the Minas Tirith city gates.

Origin
Not much is known about where these great beasts came from. Although in the video game The Battle for Middle Earth they are called yurgs and are bred in the Misty Mountains and used by the dwarves as pack animals, it's more likely they came from the far South, maybe from Dark Land or Far Harad. However, it is unlikely they came from any western lands controlled by the Free Peoples.