Part 7/8:
With their ranks diminished and the guardian recalled to Minas Tirith, the remaining soldiers were ultimately overrun by a faction known as the Rangers, who had once served Sauron. This allowed them to claim Isengard while ignoring Orthanc, which they could not penetrate.
The timeline of ownership of Isengard shifted from a Gondorian garrison to the Terror-folk, eventually leading to Saruman’s appointment by the joint forces of Rohan and Gondor. Trust was placed in Saruman, believing he would safeguard the tower—an assumption that would later prove misguided.
After Saruman’s betrayal and downfall, Aragorn reclaimed Isengard but assigned it to Treebeard and the Ents, ensuring the protection of its secrets, particularly Orthanc, which held the seeing-stone.