Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

125. But while they were disputing, the news arrived that the Illyrians had just betrayed Perdiccas¹ and joined Arrhibaeus, whereupon they both resolved to retreat; for they were afraid of the Illyrians, who are a nation of warriors. Owing to the dispute nothing had been determined respecting the time of their departure. Night came on, and the Macedonians and the mass of the barbarians were instantly seized with one of those unaccountable panics to which great armies are liable². They fancied that the Illyrians were many times their real number, and that they were close at their heels; so, suddenly betaking themselves to flight, they hastened homewards. And they compelled Perdiccas, when he understood the state of affairs, which at first he did not, to go away without seeing Brasidas, for the two armies were encamped at a considerable distance from one another. [2] At dawn Brasidas, finding that Arrhibaeus and the Illyrians were coming on and that the Macedonians had already decamped, resolved to follow them. So he formed his hoplites into a compact square, and placed his light-armed troops in the centre. He selected the youngest of his soldiers to run out upon the enemy at whatever point the attack might be made. [3] He himself proposed during the retreat to take his post in the rear with three hundred chosen men, meaning to stop the foremost of his assailants and beat them off. [4] Before the Illyrians came up he exhorted his soldiers, as far as the shortness of the time permitted, in the following words:—