The Battle of Isengard was the desolation the Ents and the Huorns, led by Treebeard, inflicted upon Saruman's stronghold of Isengard during the War of the Ring.

Saruman had at one time been a friend of Treebeard, walking in Fangorn Forest and showing appreciation for living things. But when his heart turned to the shadow, and thought of obtaining the One Ring began to enter his mind, he feigned allegiance with Sauron and he began to prepare a great army.

In order to fuel the fires in the great caverns that were dug in the Ring of Isengard, Saruman cut down all of the trees within that ring and many others besides, so earning him the hatred of the Ents and the Huorns.

At Treebeard's bidding the Ents and Huorns marched upon Isengard and unleashed their fury upon it, utterly destroying Isengard. The tower of Orthanc remained and for a time Saruman and his servant Gríma were imprisoned inside.