On the way south he met with no resistance except from the strong citadel at Gaza, which withstood him for two months and was finally taken by storm. The march to Egypt could now be safely undertaken, as the whole sea coast from the Hellespont south was in the hands of the Greeks. Egypt itself had no love for its Persian masters. It had not long before been autonomous for fifty years, and it had been brought back under the régime of the Great King under circumstances of repression that made its inhabitants greet Alexander as a liberator. The Persian governor, seeing the folly of resistance, gave up the strong places, and Alexander passed the winter in the country. During his stay he founded the only good harbor on the coast, the city which still bears his name. This undertaking was not the boastful action of a conqueror, solicitous of the praise of posterity; it was a keen-sighted scheme to divert from the Phœnician towns of Syria the control of the Mediterranean trade. Within half a century Alexandria had become a great commercial emporium, the center of Greek science and learning, and for three hundred years it continued to be the richest and largest city in the world. As the members of the old Egyptian monarchy had proclaimed themselves sons of Ammon, Alexander, in order to regularize his position in the newly conquered province, made a visit to the temple of Zeus Ammon, traveling across the desert with a small company of troops. He was greeted by the priests of the temple as the divinely accredited ruler of Egypt, but the exact words of the response of the oracle were not communicated. They were kept as a mystery, but the divine honors claimed afterwards by Alexander were always connected with this mysterious attestation of his claim that his father was no earthly parent, but Zeus himself. Darius, meanwhile, was in no position to interrupt this series of successes in Syria and in Egypt. He had no army there prepared to take the field, but he did try to interfere with the Greek lines of communication in regions more remote from the present scene of operations. Antigonus, left in Phrygia as its governor, was attacked by a force composed of some of the soldiers who had fought on the Persian side at Issus, as well as of contingents from Cappadocia and Paphlagonia. But the attempt was unsuccessful. Antigonus showed remarkable military ability, for with his small force he defeated the Persians and added to the region under him the country of Lycaonia, which had never submitted to Persian rule. In the spring of 331 Alexander left Egypt for his march to the interior of the Persian Empire, and by the middle of the summer he crossed the Euphrates near Thapsacus, and from there, taking a northerly direction through Mesopotamia, he passed the Tigris on the 20th of September.