Marsilius of Padua is conventionally seen as a thinker ahead of his time: the first secular political theorist, and the first post-classical thinker to espouse republicanism. He is presented as a scholastic precursor of the republican humanists of the Renaissance. Starting with an examination of the neglected evidence for Marsilius’s life, and the contemporary response to his best-known work, the Defensor Pacis, this new study argues that such an interpretation is quite wrong. It shows that Marsilius was not a republican, but an imperialist; and that far from being a secular political theorist, his great work Defensor Pacis is underpinned by a profound Christian understanding of history as a providentially ordained process.