Carlo Crivelli, 'Saints Peter and Paul', probably 1470s

Two saints, Peter and Paul, are deep in conversation over an open book, one pointing out a particular passage to the other. This painting comes from a polyptych painted for the high altar of the parish church of Porto San Giorgio, the harbour of the city of Fermo on the east coast of Italy.

We can identify Peter and Paul, who shared a feast day and were usually shown together in medieval art, by how they look. As apostles, both carry books and have bare feet and haloes. Saint Peter is conventionally shown as an old man with tonsured grey hair and a beard. He has a weighty set of keys hanging from his left wrist: the keys to the Kingdom of Heaven, given to him by Christ (Matthew 16: 18–19). Saint Paul, who is younger with dark hair and a long beard, leans on the sword used to execute him. Shown together they symbolise the Catholic Church: Paul as Apostle to the Gentiles (non-Jews) and Peter as Vicar of Christ and first Bishop of Rome (that is, pope).

Although these saints are biblical figures, the detail of how they are shown would have had immediate relevance to viewers in fifteenth-century Italy. Both hold manuscripts of the Gospels, elaborately bound as befitted the word of God. Saint Peter, his brow furrowed with thought, is pointing to a page in his book and instructing Saint Paul, who peers earnestly over his shoulder. Paul’s book is closed, but a protruding bookmark shows the passage in the volume that they are discussing. When this altarpiece was painted, the political issue of the day was whether the pope or the General Council had ultimate authority over the Church. Fermo was under papal control, and so here Paul is shown as subordinate to Peter, conforming with the doctrine of papal supremacy.

Crivelli was renowned for his highly individual style and way of handling materials to create a three-dimensional effect in his paintings. Here we can see how he emphasised important parts of the painting: the haloes, Peter’s keys, Paul’s sword and the brass furnishings of the books have been built up in layers of gesso and then carved so that they stand out from the flat surface.

The altarpiece probably remained at Porto San Giorgio until the church was demolished in 1803. It was split up in the mid-nineteenth century. Originally, a painting of the Virgin and Child (now in Washington) appeared in the centre of the polyptych, with this panel on the left and Saint George and the dragon (now in Boston) on the right. The whole was topped by an image of the Lamentation, now in Detroit.