The Creed plays a fundamental role in the rite of Baptism, for it summarizes the profession of faith to which the catechumen adheres. Even though a rather unusual theme in Italian painting, in Siena it was a frequent topic, as attested by the inlaid choir stalls in the interior chapel of Palazzo Pubblico, made between 1415 and 1428 by Niccolò dei Cori, and the frescoes in the Chapel of the Nail in Santa Maria della Scala hospital, painted in 1449 by the same artist who the following year painted the Articles of the Creed on the vaulted ceiling of the Baptistery, Lorenzo di Pietro, known as Vecchietta.

The Creed illustrated in the Baptistery is not the nicene Creed (the one recited during Mass), but the more synthetic formula of the apostles Creed. The frescoes cover the three cross vaults closest to the back wall of the church. There are twelve scenes, one for each article, four in every bay, starting from the one on the left and moving counterclockwise. Each web of the cross vault, which contains the illustration of an article, is accompanied in the lower right corner by an apostle and in the lower left corner by a prophet, who can be identified by the inscriptions accompanying the various characters or on their scrolls. In a sermon attributed to Pseudo-Augustine but in the Middle Ages thought to be by Saint Augustine himself, each of the apostles was said to have dictated . . .