After his period of study at Siena, Cervini traveled to Rome in the company of the delegation sent by Florence to congratulate the new Pope on his election. His father and Pope Clement VII were personal friends, and Marcello was made "Scrittore Apostolico". He was set to work on astronomical and calendar studies, a project which was intended to bring the year back into synchronization with the seasons. In 1527, he fled home after the Sack of Rome, but eventually returned and was taken into the household of Cardinal Alessandro Farnese "senior". Cervini was ordained a priest in 1535.