Antonio Ghislieri was born 17 January 1504 in Bosco in the Duchy of Milan (now Bosco Marengo in the province of Alessandria, Piedmont), Italy. At the age of fourteen he entered the Dominican Order, taking the name "Michele", passing from the monastery of Voghera to that of Vigevano, and thence to Bologna. Ordained a priest at Genoa in 1528, he was sent by his order to Pavia, where he lectured for sixteen years. At Parma he advanced thirty propositions in support of the papal chair and against the Protestant Reformation.