Topic summary
Orthanc
Extracted from the Wikipedia article Isengard.
Construction
Orthanc was built towards the end of the Second Age by men of Gondor from four many-sided columns of rock joined by an unknown process and then hardened. No known weapon could harm it. Orthanc rose to more than 500 feet (152 metres) above the plain of Isengard, and ended in four sharp peaks. Its only entrance was at the top of a high stair, and above that was a small window and balcony. It housed one of the palantírs of the South Kingdom, and was guarded by a warden.