The unbreakable black tower at the center of Isengard, raised by the Númenóreans of old from four many-sided columns of stone fused by a craft now forgotten; even the Ents, who tore Isengard's walls apart, could not mark it. One of the seven palantíri was kept in Orthanc, by which Saruman was snared by Sauron. After his defeat Saruman was imprisoned there, until Treebeard let him go; Gríma's last spiteful throw from its window delivered the palantír into the hands of the King.