Another range of inhabited hills, facing the Indian Ocean, was the south edge of the parallelogram. The eastern frontier was at first an alluvial plain called Mesopotamia, but south of Basra a level littoral, called Kuwait, and Hasa, to Gattar. Much of this plain was peopled. These inhabited hills and plains framed a gulf of thirsty desert, in whose heart was an archipelago of watered and populous oases called Kasim and Aridh. In this group of oases lay the true centre of Arabia, the preserve of its native spirit, and its most conscious individuality. The desert lapped it round and kept it pure of contact.