But Alexander showed his inventive ability before he invaded Persia; in his very first campaign undertaken to subdue a revolt in Thessaly immediately after he ascended to the throne. The Thessalians opposed him in a narrow defile. An ordinary man would have thought, as the Thessalians did, that he was checkmated. But Alexander conceived and executed the ingenious scheme of cutting a new road up the steep side of the mountain, leading his army along that road, and suddenly threatening the Thessalians in their helpless rear. Shortly afterward in Thrace he reached a defile in the mountains which it was necessary for him to pass, but which he found defended by a force that had stationed a number of war-chariots at the top, to be rolled down on the Macedonians. Alexander immediately ordered his infantry to advance up the path and to open their ranks whenever possible to let the chariots rush through; but when that could not be done to fall on their knees and hold their shields together as a sort of roof on which the chariots would slide, and from which they would roll off. This amazing story is supposed to be true; and it is said to have succeeded perfectly. Not long afterward Alexander had to cross the Danube with his army and all their equipments and attack a force of barbarians on the farther bank. This he saw he could not do by the use of any means available of an ordinary kind. Nothing daunted, he conceived and executed the scheme of floating his equipments across at night in floats made of tent skins, filled with hay. The next clear example that we find of Alexander's inventiveness was when he undertook the siege of Tyre. Tyre stood on an island of Phoenicia in the extreme eastern end of the Mediterranean Sea. It was surrounded with a wall, very thick and very high, and was separated from the shore by half a mile of deep water. To capture such a place was no small undertaking for a man who had no ships. But Alexander conceived and executed a scheme that worked successfully. In accordance with that scheme, he built a causeway that extended from the shore out toward the island on which Tyre stood. Naturally, the Tyrians obstructed his efforts by sending fireships against him and firing projectiles; and these tactics became more and more effective as the causeway approached the city. Then Alexander visited some of the jealous neighbors of Tyre that had submitted to him, and secured a fleet of some eighty ships; and these he led, as the admiral commanding, against the Tyrian harbor.