The fictional realm ruled by Saruman in J.R.R. Tolkien’s Middle-earth is Isengard. It is a fortified ring of stone surrounding the tower of Orthanc at the southern end of the Misty Mountains.
Isengard originally belonged to Gondor and guarded the Gap of Rohan. Saruman occupied it as a powerful ally of the Free Peoples, but secretly turned against them after studying the One Ring and communicating with Sauron through the palantír.
Saruman industrializes Isengard, cutting trees and breeding armies of Orcs and Uruk-hai. The Ents attack it during the War of the Ring, flooding the surrounding plain and destroying its machinery. Afterward, Isengard is restored as a green land under the stewardship of Treebeard.