The aim of this article is to provide a constitutional analysis of the passage by Polybius (1, 11, 1-3) concerning the outbreak of the First Punic War, and particularly the debate arose in Rome about the possibility to accept the Mamertines’ request for help. The ‘issue’ is represented by the role that Polybius apparently attaches to the people and not to the Senate in the final decision, a fact which had brought modern scholarship to look for which of the legislative assemblies Polybius was referring (comitia tributa or centuriata). First, it is suggested here that the debates in Rome were two and that the one which is recorded was not concerning the acceptance of the Mamertines in an alliance, but the assignment of a military command to the consul Appius Claudius. Second, that the popular intervention took place within a senatorial debate in the form of a contio as it is suggested by several elements in the language of Polybius, i.e.: the conditions of those who attended the meeting, the role played by the consul and the final decision reached by the assembly. Starting from these assumptions, a new political interpretation of the passage is proposed, namely that the consul used the will expressed by the people in the contio in order to force the Senate to give him the command that was asking, a reconstruction which is confirmed by the text of Livy (Per. 16) and which find an acceptable explanation both in that of Polybius