The Ents arrive at Isengard as Saruman's army is leaving, and they wait. After the army leaves, Treebeard bangs on the gates and shouts for Saruman to come forth. Saruman refuses, and the Ents attack. They reduce the outer walls to rubble and destroy much of what is inside the walls. Treebeard than calls an end to the attack and the Ents divert the river Isen, drowning the entire ruined fortress and all its underground furnaces and workshops. Saruman is left in the tower, surrounded by water and watchful Ents. After imprisoning Saruman, some of the Ents (including Treebeard) and Huorns keep watch.