From Arabia Encyc. Britan. II—255
Prehistoric fabulous tribes of Ad in the south, Thamood in the north, and Tasm and Jadis in the centre of the peninsula. “Very gorgeous are the descriptions given of Irem, the City of Pillars (as the Koran styles it) supposed to have been erected by Shedad, the latest despot of Ad, in the regions of Hadramaut, and which yet, after the annihilation of its tenants, remains entire, so Arabs say, invisible to ordinary eyes, but occasionally and at rare intervals, revealed to some heaven-favoured traveller.” // Rock excavations in N.W. Hejaz ascribed to Thamood tribe.