The Thracian forces had assembled in the defiles, with other troops from the northern countries, to arrest Alexander's march, and he had some difficulty in repelling them. They had got, it is said, some sort of loaded wagons upon the summit of an ascent, in the pass of the mountains, up which Alexander's forces would have to march. These wagons were to be run down upon them as they ascended. Alexander ordered his men to advance, notwithstanding this danger. He directed them, where it was practicable, to open to one side and the other, and allow the descending wagon to pass through. When this could not be done, they were to fall down upon the ground when they saw this strange military engine coming, and locking their shields together over their heads, allow the wagon to roll on over them, bracing up energetically against its weight. Notwithstanding these precautions, and the prodigious muscular power with which they were carried into effect, some of the men were crushed. The great body of the army was, however, unharmed; as soon as the force of the wagons was spent, they rushed up the ascent, and attacked their enemies with their pikes. The barbarians fled in all directions, terrified at the force and invulnerability of men whom loaded wagons, rolling over their bodies down a steep descent, could not kill.