[Sidenote: Extent of the Parthian empire.]
As to extent the kingdom of the Arsacids was far inferior, not merely to the great state of the Achaemenids, but also to that of their immediate predecessors, the state of the Seleucids. Of its original territory they possessed only the larger eastern half; after the battle with the Parthians, in which king Antiochus Sidetes, a contemporary of the Gracchi, fell, the Syrian kings did not again seriously attempt to assert their rule beyond the Euphrates; but the country on this side of the Euphrates remained with the Occidentals.
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.
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.