History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
after we had settled the rest of Boeotia and had occupied Plataea and other places of which we got possession by driving out a mixed population,[*](Strabo mentions Pelasgians, Thracians, Hyantians.) these Plataeans disdained to submit to our leadership, as had been agreed upon at first, and separating themselves from the rest of the Boeotians and breaking away from the traditions of our fathers went over to the Athenians as soon as an attempt was made to force them into obedience, and in conjunction with the Athenians did us much harm, for which they also suffered in return.
Again, they say that when the barbarians came against Hellas they were the only Boeotians who did not medize, and for this especially they plume themselves and abuse us.
We say, however, that the only reason they did not medize was because the Athenians also did not, and that, moreover, on the same principle, when the Athenians afterwards assailed all Hellas, they were the only Boeotians who atticized.[*](Ever since the Persian war medize and medium had been terms of bitter reproach in Hellas; in the mouths of the Thebans atticize and atticism have a like invidious meaning.) And yet consider the circumstances under which we each acted as we did.
For the constitution of our city at that time was, as it happened, neither an oligarchy under equal laws[*](ie. where, as at Sparta, the ὀλίγοι, or ruling class, possessed equal rights.) nor yet a democracy; but its affairs were in the hands of a small group of powerful men—the form which is most opposed to law and the best regulated polity, and most allied to a tyranny.
These men, hoping to win still greater power for themselves if the fortunes of the Persian should prevail, forcibly kept the people down and brought him in. The city as a whole was not in control of its own actions when Thebes took the course it did, nor is it fair to reproach it for the mistakes it made when not under the rule of law.