In Rome, his patron having died, Poussin, who lodged at first with Simon Vouet, fell into great distress, with the departure for Spain of his early patron Cardinal Francesco Barberini and the Cardinal's secretary, the antiquary Cassiano dal Pozzo, later a great friend and patron. The return of Barberini from Spain in 1626 stabilized and renewed the patronage of the Barberini and their circle. Two major commissions at this period resulted in Poussin's early masterwork the Barberini Death of Germanicus, partly inspired by the reliefs of the Meleager sarcophagus, and the commission for St. Peter's that amounted to a public debut, the Martyrdom of St. Erasmus (1630), with echoes of Pietro da Cortona. Falling ill at this time, he was received into the house of his compatriot Gaspard Dughet and nursed by his daughter Anna Maria to whom, in 1630, Poussin was married.
He lodged with the sculptor Francois Duquesnoy, of an equally classicizing artistic temperament, befriended Domenichino and joined an informal academy of artists and patrons opposed to the current Baroque style that formed around Joachim von Sandrart.
Among his first patrons, aside from Cardinal Francesco were: Cardinal Omodei, for whom he produced, in 1627, the Triumphs of Flora (Louvre); Cardinal de Richelieu, who commissioned a Bacchanal (Louvre); Vincenzo Giustiniani, for whom was executed the Massacre of the Innocents, of which there is a first sketch in the British Museum; Cassiano dal Pozzo, who became the owner of the first series of the Seven Sacraments (Belvoir Castle); and Paul Freart de Chantelou, with whom in 1640 Poussin, at the call of Sublet de Noyers, returned to France.