International audienceIn the speeches, but also in the narrative, Thucydides reports on the decisive collective decisions of the Peloponnesian War: the launching of the war, the choice of alliance, the Athenian expedition to Sicily, the legal proceedings against citizens or the negotiations between factions of the same city in a context of civil war. The historian treats several of these episodes in the form of antilogy in which he synthesises two contradictory points of view represented by two speakers who may disseminate - voluntarily or at their expense? - partial, biased or false information. For the most notable cases, Thucydides analyses and comments on the quality of the information available to the decision-makers. This paper propos...