A CRUSADE of the united Greeks against decrepit Persia had been advocated, in the middle of the fourth century, by Isocrates, a political pamphleteer. Isocrates appealed to Philip of Macedon (359-336 B.C.), who accepted the suggestion and, after defeating the Greeks in 338 B.C., started to organise an expedition against Persia. In 336 B.C. he was assassinated and was succeeded by his twenty-year-old son, Alexander, who considered himself the destined missionary of Greek civilisation. Alexander first quelled a rising of the Greek states, and then set out to conquer Persia. In 334 B.C. he landed in Asia Minor with a force of about forty thousand trained soldiers. It seems a small army with which to undertake the conquest of an empire, but it had been welded together by years of fighting, and was led by a supreme military genius. The Persian army, on the other hand, consisted chiefly of untrained levies differing in language and in equipment. Alexander's first act on landing in Asia Minor was to visit Troy and, by sacrificing to the gods there, to invest himself with the halo of Homer's heroes. Then, in a series of great battles, he overthrew the Persian Empire, and by the year 331 B.C. was the acknowledged ruler of the Ancient East. The next five years were spent in establishing a chain of Greek settlements and garrison posts all the way from Persia, right across Asia, and over the Khyber Pass into India. When he reached the Punjab, his Macedonians refused to accompany him further, and so he sailed down the Indus to the Indian Ocean, and then marched back to Babylon along the coast, 325-324 B.C.