Both coasts of the Persian Gulf, even the Arabian, were in possession of the Parthians, and the navigation was thus completely in their power; the rest of the Arabian peninsula did not obey either the Parthians or the Romans ruling over Egypt. [Sidenote: The region of the Indus.] To describe the struggle of the nations for the possession of the Indus valley, and of the regions bordering on it, to the west and east, so far as the wholly fragmentary tradition allows of a description at all, is not the task of our survey; but the main lines of this struggle, which constantly goes by the side of that waged for the Euphrates valley, may the less be omitted in this connection, as our tradition does not allow us to follow out in detail the circumstances of Iran to the east in their influence on western relations, and it hence appears necessary at least to realise for ourselves its outlines. Soon after the death of Alexander the Great, the boundary between Iran and India was drawn by the agreement of his marshal and coheir Seleucus with Chandragupta, or in Greek Sandracottos, the founder of the empire of the Indians. According to this the latter ruled not merely over the Ganges-valley in all its extent and the whole north-west of India, but in the region of the Indus, at least over a part of the upland valley of what is now Cabul, further over Arachosia or Afghanistan, presumably also over the waste and arid Gedrosia, the modern Beloochistan, as well as over the delta and mouths of the Indus; the documents hewn in stone, by which Chandragupta’s grandson, the orthodox Buddha-worshipper Asoka, inculcated the general moral law on his subjects, have been found, as in all this widely extended domain, so particularly in the region of Peshawur.[15] The Hindoo Koosh, the Parapanisus of the ancients, and its continuation to the east and west, thus separated with their mighty chain--pierced only by few passes--Iran and India. But this agreement did not long subsist. [Sidenote: Bactro-Indian empire.] In the earlier period of the Diadochi the Greek rulers of the kingdom of Bactra, which took a mighty impulse on its breaking off from the Seleucid state, crossed the frontier-mountains, brought a considerable part of the Indus valley into their power, and perhaps established themselves still farther inland in Hindostan, so that the centre of gravity of this empire was shifted from western Iran to eastern India, and Hellenism gave way to an Indian type. The kings of this empire were called Indian, and bore subsequently non-Greek names; on the coins the native Indian language and writing appear by the side, and instead, of the Greek, just as in the Partho-Persian coinage the Pahlavi comes up alongside of the Greek. [Sidenote: Indo-Scythians.]