History of the Peloponnesian War

For there were both Argilians that dwelt in the same city (now Argilus is a colony of the Andrians), and others, that contrived this, induced thereunto some by Perdiccas and some by the Chalcideans.

But above all the Argilians, being of a city near unto it, and ever suspected by the Athenians, and secret enemies to the place, as soon as opportunity was offered and Brasidas arrived (who had also long before dealt underhand with as many of them as dwelt in Amphipolis to betray it), both received him into their own city, and revolting from the Athenians, brought the army forward the same night as far as to the bridge of the river.

The town stood not close to the river, nor was there a fort at the bridge then as there is now; but they kept it only with a small guard of soldiers. Having easily forced this guard, both in respect of the treason and of the weather, and of his own unexpected approach, he passed the bridge and was presently master of whatsoever the Amphipolitans had that dwelt without.

Having thus suddenly passed the bridge, and many of those without being slain, and some fled into the city, the Amphipolitans were in very great confusion at it; and the rather because they were jealous one of another.

And it is said that if Brasidas had not sent out his army to take booty, but had marched presently to the city, he had in all likelihood taken it then. But so it was that he pitched there and fell upon those without;

and seeing nothing succeeded by those within, lay still upon the place.

But the contrary faction to the traitors being superior in number, whereby the gates were not opened presently, both they and Eucles the general, who was then there for the Athenians to keep the town, sent unto the other general, Thucydides, the son of Olorus, the writer of this history, who had charge in Thrace, and was now about Thasos (which is an island and a colony of the Parians, distant from Amphipolis about half a day's sail), requiring him to come and relieve them.

When he heard the news, he went thitherwards in all haste with seven galleys, which chanced to be with him at that time. His purpose principally was to prevent the yielding up of Amphipolis; but if he should fail of that, then to possess himself of Eion [before Brasidas' coming].