Son of a notary in the service of the Colonna family of Naples, Giulio Mazarini attended the Jesuit College in Rome. In 1619, Mazarini (b. 1602) travelled to Spain as the chamberlain to Girolamo Colonna, principe di Paliano and heir of the Colonna family, and in 1624 he was appointed a captain in the prince’s regiment, raised in the service of the Pope to maintain the fragile peace in the Valtellina.
A wordly and inquisitive young man, Mazarini is short but handsome and well-proportioned. He has a reputation as a gambler, reputedly wracking up considerable debts during his brief trip to Spain.