Contrarily to most traditional accounts on the foundation of the Republic, Dionysius describes the passage from the Tarquins’ monarchy to the Republic as a lawful constitutional reform, in which L. Junius Brutus played a pivotal role. In my paper I analyze the speech that Brutus delivers to the Roman patricians to endorse the establishment of a new government in Rome. The new constitution, although remaining essentially monarchical, will keep its autocratic nature concealed from the people. Throughout this paper, I show how Dionysius in his presentation of Brutus picked up elements both related to the senatorial propaganda against M. Junius Brutus — Caesar’s murderer, who claimed descent from L. Brutus and the tyrannicide Ahala — and, at the same time, the character of Augustus’s newly-founded government. This account may thus be regarded as Dionysius’ own elaboration of Augustus’s constitutional reform.