When Leonardo reported the small sketch of the church of santosano on the famous bird's eye view of Montalbano (RL 12685), he must have had before him a building different than the great Romanesque church that had governed the ecclesiastical territory of Greti during the High Middle Ages. The volume of the building had been reduced by a good bit during the 14th century, and then, when the church passed to dependency under the Certosa del Galluzzo of Florence in 1478, it was further modified. With the arrival of the community of monks, the church had to be renewed for questions of liturgical order. On the outside, a large porch with a pavilion roof was built, resting on cross vaults, with pediments inserted into the facade remain. The lunette of the portal, furnished with a new molded architrave, was adorned with a fresco depicting La Vergine e il Bambino fra i santi Giovanni Battista e Ansano. Inside, next to the entrance portal, Leonardo could have seen the fine hexagonal baptismal font in marble worked with bean-motif attributed to Baccio da Montelupo. At the end of the 16th century, the rear part of the building was modified for liturgical reasons: the original semicircular apse was replaced by the rectangular apse that today defines the choir. An image of the parish church of Greti dating back to this period is the one we find represented on the map of the Capitani di Parte Guelfa, bearing the toponym S. Giovanni in Greti et detto S. Sano. Even though the drawing is certainly stylized, it does, however, present some interesting details, such as the basilica plan with three naves of the church, seen in three-quarter view, with a tiered facade and a small bell gable. Above the central portal, we can see the window, now replaced by the oculus, and there is no remaining trace of the portico, perhaps no longer standing after the end of the 16th century. This, in general terms, is the aspect the parish church of Greti must have had during Leonardo’s time.