In August 1502, the fifty-year-old Leonardo was appointed military architect and engineer to Cesare Borgia, son of Pope Alexander VI and commander of the Papal army. Over the next few months Leonardo surveyed Borgia’s strongholds to the north and east of Florence, creating his most impressive surviving map, of the town of Imola.

After leaving Borgia’s service Leonardo returned to Florence, where he continued to make maps. Some were presumably commissioned by the Florentine government, such as surveys of the Valdichiana in southern Tuscany. Others record Leonardo’s proposal to construct a canal to bypass the river Arno, or are expressions of his interest in geological processes.