History of the Peloponnesian War
Thucydides
Thucydides. The history of the Peloponnesian War, Volume 1-2. Dale, Henry, translator. London: Heinemann and Henry G. Bohn, 1851-1852.
who, having received them, took them to Athens. On their arrival the Athenians, being afraid that if Aristeus escaped he might do them still more mischief, (for even before this he had evidently conducted all the measures in Potidaea and their possessions Thrace-ward,) without giving them a trial, though they requested to say something [in their own defence], put them to death that same day, and threw them into pits; thinking it but just to requite them in the same way as the Lacedaemonians had begun with; for they had killed and thrown into pits the merchants, both of the Athenians and their allies, whom they had taken on board trading vessels about the coast of the Peloponnese. Indeed all that the Lacedaemonians took on the sea at the beginning of the war, they butchered as enemies, both those who were confederates of the Athenians and those who were neutral.
About the same time, when the summer was drawing to a close, the Ambraciots, with their own forces and many of the barbarians whom they had raised, made an expedition against Argos in Amphilochia, and the rest of that country.
Now their enmity against the Argives first arose from the following circumstances.
Argos in Amphilochia and The rest of the country was colonized by Amphilochus the son of Amphiaraus, when he returned home after the Trojan war, and was not pleased with the state of things at Argos;