QAIS, an island in the Persian gulf lying about 1 o m. off the mainland of Persia in 54° E. ; it is the site of a trade emporium of great importance in former times. The island measuring io m. by 5 m., rises 120 f t. above sea level to a plateau and is bare of vegetation except for small patches of cultivation and a few date groves and stunted herbage. It is surrounded by a reef and pearl banks. The normal population is estimated at about 2,000 chiefly Arabs of the Al Ali tribe, who largely engage in pearl fishing.
Qais is an arabicized form of the Persian Kish; and is the Kataia of Arrian. In the Mohammedan period it formed a part of the province of Fars, but it was only in the later middle ages that the place attained importance, when a prince of South Arabian origin obtained possession of it, built a fleet there, and gradually extended his power. He captured Siraf (modern Tahiri 27° 4o' N., 20' E.) which was then the principal emporium of the Persian Indian-Chinese trade. Siraf gradually—in the first half of the century—became more and more deserted under the suze rainty of the princes of Qais, as they diverted the very consider able trade from the captured Persian sea-port to their own island, and finally Qais supplanted Siraf.
At its period of greatest power, the dynasty of Qais also ruled over the district of Oman on the opposite Arabian shore. The Rabbi Benjamin of Tudela visited Qais between A.D. 1164-73, and noted the rich market of the island whose chief business was the exchange of Persian, Mesopotamian, Arabian and Indian manufactures and produce. The site of the old city is marked by the ruins known as Harira on the north coast. Qais in turn lost its importance—f or what reason is not precisely known—some where in the century, and its trade passed to Hormuz.
See W. Ouseley, Travels in various countries of the East, vol. i. (1819) ; A. W. Stiffe, "Ancient trading centres of the Persian Gulf. Kais." Geogr. J., 1896, VII.; A. T. Wilson, The Persian Gulf (1928). (P. Z. C.)