There was constant communication between the Grecian and Persian nations. We learn that it was not uncommon for Grecian generals to take service under the Persian Satraps, tempted by the liberal recompence with which their services were rewarded. About the year 356 B.C. this system of Greeks accepting service under Persian Satraps nearly caused the outbreak of war between Greece and Persia--Chares, a Grecian commander, having assisted with his fleet and men, Artabanus, the Satrap of Propontis, who was then in revolt against the Persian king. But before this, during the great plague which desolated Athens in 430 B.C., and which also extended to Persia, Hippocrates was invited to go to the Persian Court; and it is on record that Ctesias was for seventeen years physician at the Persian Court about 400 B.C., during which period he wrote his history of Persia, and an account of India, which Professor Wilson, in a paper read to the Ashmolean Society of Oxford, has shown to contain notices of the natural productions of the country, “which, although often extravagant and absurd, are, nevertheless, founded on truth.” There were, too, Grecian soldiers employed as paid auxiliaries, and a colony of Greeks who had been taken prisoners of war was founded within a day’s journey of Susa. The great expedition to Persia, and the graphic description of the retreat of the “ten thousand” Greeks, given by Xenophon in his Anabasis, must have been well known to Alexander the Great when he set out on his career of conquest. He overthrew the Persian empire in 331 B.C., having destroyed Tyre and subdued Egypt in the previous year and carried his triumphant progress to the banks of the Indus, and there he “held intercourse with the learned sages of India.” On Alexander’s death Seleucus succeeded to the throne of Persia in 307 B.C., and not long after he forced his way beyond the Indus, and ultimately as far as the sacred river Ganges. He formed an alliance with the Indian king Sandrocottus (otherwise known as Chandra-gupta), which was maintained for many years, and it is said, also, that he gave his daughter in marriage to the Indian king, and aided him with Grecian auxiliaries in his wars. He sent an expedition by sea, under the command of Patrocles his admiral, who visited the western shores of India, and a little later he despatched an embassy under Megasthenes and Onesicrates, the former of whom resided for some years at the “great city” of Palibothra (supposed to be Patna). Not long after Megasthenes was at Palibothra, Ptolemy Philadelphus sent an expedition overland through Persia to India, and later Ptolemy Euergetes, who lived between 145-116 B.C., sent a fleet under Eudoxius on a voyage of discovery to the western shores of India, piloted, as is said, by an Indian sailor who had been shipwrecked, and who had been found in a boat on the Red Sea. Eudoxius reached India safely, and returned to Egypt with a cargo of spices and precious stones.