Though many cardinals opposed the promotion, in 1505 Alidosi was created cardinal-priest of Santi Nereo e Achilleo, opting for the title of S. Cecilia on 11 August 1506. He served as intermediary between Michelangelo Buonarroti and Pope Julius II and, in 1506, signed on behalf of the pope the contract for the ceiling frescoes of the Sistine Chapel, later doing the same for the statue of the Pope in Bologna. He also served as Cardinal protector of England within the college. He was a protector of Desiderius Erasmus and patron of the arts.
