Next to correctness of drawing and dignity of conception, Poussin valued expression in painting. He ranked Domenichino next to Raffaelle for this quality, and not long after his arrival at Rome, he set about copying the Flagellation of St. Andrew, painted by that master in the church of S. Gregorio, in competition with Guido, whose Martyrdom of that Saint is on the opposite side of the same church. Poussin found all the students in Rome busily copying the Guido, which, though a most beautiful work, lacks the energy and expression which distinguish the Flagellation; but he was too sure of his object to be led away by the crowd. According to Felibien, Domenichino, who then resided at Rome, in a very delicate state of health, having heard that a young Frenchman was making a careful study of his picture, caused himself to be conveyed in his chair to the church, where he conversed some time with Poussin, without making himself known; charmed with his talents and highly cultivated mind, he invited him to his house, and from that time Poussin enjoyed his friendship and profited by his advice, till that illustrious painter went to Naples, to paint the chapel of St. Januarius.