The theme of the Mass of Saint Gregory appears in art only from the 15th century. It is based on the legend of Saint Gregory the Great (540-604): while the saint was celebrating mass in the Roman Basilica of the Holy Cross in Jerusalem, Christ appeared to him with the wounds incurred after the Crucifixion and with the instruments of torture. We see the Man of Sorrows as a half-figure (the type of the Imago Pietatis) above the altar table, with blood flowing from the wound in his side. Gregory is kneeling with two deacons before the altar, from behind a priest is bringing him the Papal tiara. The message of this scene lies in the confirmation of the true presence of the body and blood of the Lord in the ceremony at the altar.