History of the Peloponnesian War

The next summer Alcibiades sailed with twenty ships to Argos and seized the suspected persons still left of the Lacedaemonian faction to the number of three hundred, whom the Athenians forthwith lodged in the neighboring islands of their empire. The Athenians also made an expedition against the isle of Melos with thirty ships of their own, six Chian, and two Lesbian vessels, sixteen hundred heavy infantry, three hundred archers, and twenty mounted archers from Athens, and about fifteen hundred heavy infantry from the allies and the islanders.

The Melians are a colony of Lacedaemon that would not submit to the Athenians like the other islanders, and at first remained neutral and took no part in the struggle, but afterwards upon the Athenians using violence and plundering their territory, assumed an attitude of open hostility.