Saruman used his influence through the traitor Grima Wormtongue to weaken Théoden. Saruman then launched an invasion of Rohan, with victory in early battles at the Fords of Isen, killing Théoden's son, Théodred. Saruman was defeated at the Battle of the Hornburg, where the tree-like Huorns came from the forest of Fangorn to help the Rohirrim.