In pursuit of this opinion, he reduced the barbarians to tranquility, and put an end to all fear of war from them, by a rapid expedition into their country as far as the river Danube, where he gave Syrmus, king of the Triballians, an entire overthrow.
And hearing the Thebans were in revolt, and the Athenians in correspondence with them, he immediately marched through the pass of Thermopylae, saying that to Demosthenes who had called him a child while he was in Illyria and in the country of the Triballians, and a youth when he was in Thessaly, he would appear a man before the walls of Athens.
Alexander then returned to Macedonia in the hope of being able to begin his Persian expedition in the spring of B.C. 335; but reports of disturbances among the Thracians and Triballians diverted his attention to that quarter. After acquiring a large booty he regained the banks of the Danube, and thence marched against the Illyrians and Taulantians, whom he speedily reduced to obedience.