The Lombard architect Gasperino di Antonio built the Chapel of St. Johnn the Baptist between 1506-1509 on the spot where there was the ancient church of “St. Johnn of the market” (San Giovanni del mercato). Interesting traces of the previous building are visible below the floor. The wooden stalls (1508-1509) carved by Antonio di Mercatello of the Marche were the first internal decoration. The same artist was responsible for the wooden shutters of the Guild of the Money Changer’s portals.A few years later (1512) Mariano di Ser Austerio carved the frontal altar.
The paintings over the walls were the final work. This was commissioned to Giannicola di Paolo. He carried out his work very slowly (the last frescoes were painted between 1528-1529). Beginnig with G. B. Cavalcaselle (1866) all the critics underlined that the vault decoration show traces of Perugino’s strong influence (the Eternal Father is clearly inspired by the one of Perugino in the Audience Hall). The remarkable difference of style between the vault and the walls is the result of the painter’s evolution of language and it is not associated with possible contributions from his assistants. In the beginning Giannicola di Paolo was strictly following the rigid Perugino’s canons. Later he progressively broke away from them and approached the style of Raphael (the images of the Sybils are similar to those of the Master in Rome), of the Sienes Pacchia and Sodoma and of the Tuscan Andrea del Sarto. Recently they recognised possible links with the Northern Italy painting, particularly with that of the artist Pordenone who was working in Perugia around 1516. The high level altar-piece reveals a special attention for the art of Luca Signorelli. The bright colour of the walls, emphasized by abundance of fine gold over the altar and the vault, seemed to be necessary in order to illuminate the semi-darkness of the place since light comes in only from the entrance portal.