Before setting off on his expedition, he contrived to obtain a considerable force from among the Gauls as auxiliaries. Antigonus, also, had Gauls in his service, for they themselves were divided, as it would seem, in respect both to their policy and their leaders, as well as the Macedonians; and Antigonus, taking advantage of their dissensions, had contrived to enlist some portion of them in his cause, while the rest were the more easily, on that very account, induced to join the expedition of Pyrrhus. Things being in this state, Pyrrhus, after completing his preparations, commenced his march, and soon crossed the Macedonian frontier.
As was usually the case with the enterprises which he engaged in, he was, in the outset, very successful. He conquered several cities and towns as he advanced, and soon began to entertain higher views in respect to the object of his expedition than he had at first formed. Instead of merely plundering the frontier, as he had at first intended, he began to think that it would be possible for him to subdue Antigonus entirely, and reannex the whole of Macedon to his dominions. He was well known in Macedon, his former campaigns in that country having brought him very extensively before the people and the army there. He had been a general favorite, too, among them at the time when he had been their ruler; the people admired his personal qualities as a soldier, and had been accustomed to compare him with Alexander, whom, in his appearance and manners, and in a certain air of military frankness and generosity which characterized him, he was said strongly to resemble. Pyrrhus now found, as he advanced into the country of Macedonia, that the people were disposed to regard him with the same sentiments of favor which they had formerly entertained for him. Several of the garrisons of the cities joined his standard; and the detachments of troops which Antigonus sent forward to the frontier to check his progress, instead of giving him battle, went over to him in a body and espoused his cause. In a word, Pyrrhus found that, unexpectedly to himself, his expedition, instead of being merely an incursion across the frontiers on a plundering foray, was assuming the character of a regular invasion. In short, the progress that he made was such, that it soon became manifest that to meet Antigonus in one pitched battle, and to gain one victory, was all that was required to complete the conquest of the country.