History of the Peloponnesian War

Meanwhile, as they were disputing, it was announced that the Illyrians had betrayed Perdiccas and taken sides with Arrhabaeus; consequently, because of their fear of these people, who were warlike, both generals now agreed that it was best to retreat. But in consequence of their dispute nothing had been determined as to when they should set out; and when night came on the Macedonians and the mass of the barbarians immediately took fright, as large armies are wont to be smitten with unaccountable panic, and thinking that the advancing enemy were many times more numerous than they really were and were all but on them, betook themselves to sudden flight and hastened homewards. Perdiccas, who at first was not aware of their movement, was compelled, when he did learn of it, to go away without seeing Brasidas; for they were encamped far away from each other.

But at daybreak, when Brasidas saw that the Macedonians had already decamped and that the Illyrians and Arrhabaeus were about to come against him, he formed his hoplites into a square, put the crowd of light-armed troops in the centre, and was himself intending to retreat.