Their first known settling-place was west of the later Gap of Rohan between the Misty Mountains and the White.
After Calenardhon was given to the Éothéod by Cirion, Steward of Gondor, and became Rohan, Isengard was the sole fortress retained by Gondor north of the Ered Nimrais (excluding Anórien), although Gondor almost forgot about it.