When he was twenty his father decided to send him away from the bad influences of Rome. Giulio accompanied Girolamo Colonna, one of the sons of Filippo I Colonna, who was eighteen, to the Complutense University of Madrid (then located in Alcalá de Henares) in Spain. He studied law with Girolamo during the daytime and in the evenings continued to gamble and again was in debt. A notary who had advanced some cash to cover gaming debts urged the charming and personable young Mazarino to take his daughter as bride, with a substantial dowry, and Giulio accepted. Girolamo Colonna wrote urgently to his father in Rome, and Giulio was ordered to return immediately to Rome, without his fiancée.