A Pope (Saint Gregory?) and Saint Matthias

Saint Matthias is an unusual guest on an altarpiece. He was the apostle chosen by lot to replace Judas and was never widely venerated, yet Santa Maria Maggiore in Rome held his buried relics and showed him in its mosaics. This panel was painted for that church around 1428 or 1429, and he holds the axe of his martyrdom. The pope beside him is probably Gregory the Great, who by legend led a procession to Santa Maria Maggiore during the plague of 590 to ask for the Virgin's help. Martin V, the reigning pope who may have ordered the altarpiece, was especially devoted to Gregory, though the National Gallery keeps a question mark in the title. Masaccio's Saints Jerome and John the Baptist were painted on the back of this panel. That red cope looks dull today. Masolino laid it over silver leaf under a red glaze, and it once gleamed.