The Tower of Isengard, built by the men of Gondor at the end of the Second Age. Its name had a dual meaning - in Elvish it translated as 'Mount Fang', ultimately from the roots orod 'mountain' and anca 'jaws'. The second (and original) meaning, 'cunning mind', was Rohirric and comes from the Old English orþanc.

The tower stood in the Ring of Angrenost, and was built of four pinnacles of hard black stone, joined together into a single structure. Just below the summit, the pinnacles opened out into gaping horns, sharp as the points of spears. Between the horns was a narrow floor of polished stone, engraved with strange signs.

In the Third Age, Gondor withdrew its forces from the Isengard area, and the tower then remained locked for many years. However, one of the palantíri was locked away within it, and it was this power that attracted Saruman to Orthanc towards the end of the Third Age. In TA 2953, Saruman came to Beren of Gondor, the Ruling Steward of that time, under a guise of friendship, and Beren gave him the Keys of Orthanc. Saruman then occupied the tower until the time of the War of the Ring.

During the War of the Ring, the walls around Orthanc were destroyed by the Ents, and the tower of Orthanc was restored to Gondorian ownership.