By this time, the causeway was well protected with catapults and war-engines of various kinds, and had been carried close up to the island. Yet little actual damage could be done to Tyre, because of the height and thickness of the walls, and because Alexander's galleys that he had equipped with war-engines could not get close enough, by reason of large boulders under water. Alexander then equipped certain galleys with windlasses to root up the boulders, the galleys being fitted with chain cables to prevent divers from cutting them. Tyre was soon afterwards reduced to a purely passive defense and consequent surrender. The story of the siege of Tyre, if read in the light of the conditions of the comparative barbarism of the world in those days, is a record of inventiveness, on the part of Alexander, so convincing and complete, as to entitle Alexander to a place in the first rank among the inventors of our race. Shortly afterward Alexander reached the town of Gaza, the great stronghold of the Philistines. It stood on high ground, and was more than two miles from the sea. Alexander's engineers reported to him that, as the fleet could not assist them, and as the walls were themselves very high and stood on a high hill, the walls could never be stormed. Things looked serious. They were serious; and failure would then have come to any man, except a man like Alexander. He cut the Gordian knot by ordering that ramparts be thrown up as high as the top of the walls, and war engines placed on the ramparts. This was done, and the city was taken. Alexander's campaigns in Egypt, and afterward in western Asia, were characterized by the same quickness and daring, both in conception and in execution, that had marked his opening campaigns in Greece. Later, when advancing toward Persia, he encountered a tribe of hillsmen in the Uxian Pass, who, like the Thessalians and the Thracians, thought they had blocked his passage by opposing him in so narrow a defile. Alexander literally "circumvented" them by making a night march over a difficult mountain pass, and astonishing them by an attack on their rear the following morning. Shortly afterward a like situation presented itself, when an army opposed him in a narrow defile called the Persian Gates, that was fortified with a wall. Alexander soon realized that the position of his enemy was impregnable. He learned, however, that there was a path that led around the pass, though it was exceedingly dangerous, particularly to men in armor and to horses, and especially at that time, when snow and ice were on the ground. He again utilized his former invention (circumvention) and with his former success; though the conditions under which it was accomplished were much more difficult. The four examples just given of literally circumventing an uninventive enemy illustrate in the simplest form the influence of invention on military history.