Masaccio’s Saints Jerome and John the Baptist and Masolino’s A Pope, Saint Gregory (?) and Saint Matthias were painted on either side of the same piece of wood and formed the left-hand panel of a double-sided altarpiece made for the church of Santa Maria Maggiore in Rome.

Giorgio Vasari, the sixteenth-century writer and artist who wrote biographies of Italian artists from the thirteenth century onwards, visited the church with Michelangelo in 1568. He described the altarpiece in his account of the life of Masaccio, saying he saw 'several panels' painted with four saints and 'in the centre the "Miracle of the Snow"', which explained the church's foundation in the fourth century. A Roman couple wished to donate their wealth in honour of the Virgin Mary and prayed for guidance on how to dispose of their riches. On the evening of 5 August, snow began to fall on the Esquiline hill; the couple built the church on that spot and dedicated it to the Virgin. The miracle and the church's foundation are still celebrated on that date.

Vasari probably only saw one side of the altarpiece because he did not describe its reverse. In fact, although he says he saw four painted saints, he only mentions the Miracle of the Snow and the figure of Saint Martin (Pope Martin V) who was 'drawn as if from life'. A panel showing Saint Martin and Saint John the Evangelist (now in Philadelphia Museum of Art) is most likely the picture Vasari saw. The other two saints were probably Saints Jerome and John the Baptist, originally positioned to the left of the central panel.

The other side of the central panel was painted with the Assumption (the moment that the Virgin ascended to heaven after her death); the feast was also important to Santa Maria Maggiore and is still celebrated there on 15 August. This was flanked by  A Pope (Saint Gregory?) and Saint Matthias (on the reverse of Saints Jerome and John the Baptist) and another panel showing Saints Peter and Paul (the reverse of Saint Martin and Saint John the Evangelist, now also in Philadelphia).

Vasari described the altarpiece's location as a small chapel near the sacristy. It is likely that this was a chapel behind the church's main altar, reserved for the worship of the church's canons. This chapel belonged to the esteemed Roman Colonna family and was dedicated to Saint John the Baptist. One side of the altarpiece would have been visible by those within the chapel, while the other side -- its public face -- was that seen by Vasari.

The altarpiece may have been commissioned by Pope Martin V who was a member of the Colonna family. They had a long association with the church, dating to the thirteenth century when Cardinal Jacopo Colonna made additions and decorations to the building and founded two family chapels, including the one where this altarpiece was once displayed.

Masaccio and Masolino often worked together, collaborating most famously on the fresco cycle in the Brancacci chapel, Florence, in the early 1420s. They are distinguishable here by their technique. Masaccio has used a green base paint, known as green earth, beneath the flesh colours while Masolino used only vermilion (a red pigment) and white paint. Furthermore, Masaccio has used only egg to mix his paints whereas Masolino has also included oil.

Masolino painted both sides of the central panel and the image of Gregory and Matthias, while Masaccio painted Saint Jerome and John the Baptist. Masaccio died in Rome in 1428/9, probably in a plague epidemic. After his death, Masolino seems to have completed the side panel showing Saint John the Evangelist and Saint Martin, with Saints Paul and Peter on the reverse.

Style: Gothic, Early Renaissance