History of the Peloponnesian War
Thucydides
Thucydides. History of the Peloponnesian War. Crawley, Richard, translator. London and Toronto: J. M. Dent and Sons Ltd.; New York: E. P. Dutton and Co., 1914.
With this answer they went away, and he took the advice of his escort, and pushed on without halting, before a greater force might gather to prevent him. Thus in the day that he set out from Melitia he performed the whole distance to Pharsalus, and encamped on the river Apidanus; and so to Phacium, and from thence to Perrhaebia.
Here his Thessalian escort went back, and the Perrhaebians, who are subjects of Thessaly, set him down at Dium in the dominions of Perdiccas, a Macedonian town under Mount Olympus, looking towards Thessaly.
In this way Brasidas hurried through Thessaly before any one could be got ready to stop him, and reached Perdiccas and Chalcidice.
The departure of the army from Peloponnese had been procured by the Thracian towns in revolt against Athens and by Perdiccus, alarmed at the successes of the Athenians. The Chalcidians thought that they would be the first objects of an Athenian expedition, not that the neighbouring towns which had not yet revolted did not also secretly join in the invitation; and Perdiccas also had his apprehensions on account of his old quarrels with the Athenians, although not openly at war with them, and above all wished to reduce Arrhabaeus king of the Lyncestians.
It had been less difficult for them to get an army to leave Peloponnese, because of the ill fortune of the Lacedaemonians at the present moment.