The Art Archive/Antiquarium Castellamare di Stabia, Italy/Dagli Orti

A UNITED FRONT. Peter (right) and Paul embrace on this fourth-century ivory belt buckle discovered in the ancient seaside town of Stabia, 3 miles south of Pompeii. In the fourth century, when Constantine made Christianity legal, the factions of the church—including the followers of Paul and Peter—were forced to unite. In art and literature, the two men were, for the first time, shown as partners. Around the same time, Paul was inserted into images of Simon Magus’s fall. He generally appears in prayer, beside Peter.

The hair styles of the two apostles—Paul balding, with a long beard, Peter with shorter curly hair—quickly became the standard in art, as reflected in the paintings throughout this article.