Orthanc

In J. R. R. Tolkien's fictional universe of Middle-earth, Orthanc is the black tower of Isengard. Its name is Sindarin for "Mount Fang".\n Orthanc was built during the Third Age by the Númenóreans of Gondor out of a single piece of stone by an unknown process and then hardened. No known weapon could harm it. Orthanc rose up 500 feet above the plain of Isengard, and ended in three sharp peaks. Its only entrance was at the top of a high stair, and above that was a small window. Orthanc housed one of the Palantíri of the South Kingdom, and was guarded by a special warden until Isengard was mostly abandoned by Gondor. After that the tower was locked. When Beren, Steward of Gondor gave Isengard to Saruman, he also gave the keys to Orthanc to the Wizard. Saruman made it his base of operations during his search for the One Ring and later his attack on Rohan during the War of the Ring. After Saruman's defeat he was confronted by Théoden King, Gandalf and Aragorn, at which time Gríma, Saruman's servant, threw the Palantír at the group trying to kill them. Saruman was then locked in Orthanc and guarded by Treebeard, who eventually let him go. During the Fourth Age Orthanc was searched by Aragorn King Elessar, and he found there many heirlooms of Isildur, among them the original Elendilmir, the Star of Arnor, which proved that Saruman had found (and probably destroyed) Isildur's remains. Aragorn also found there a casket which obviously had been intended to hold the Ring.