Inside da Vinci and Machiavelli’s Plot to Weaponize a River

In 1503, Leonardo da Vinci began painting a portrait of Lisa Gherardini del Giocondo, the wife of a wealthy Florentine silk merchant. With its enigmatic smile, the “Mona Lisa” would become one of the most famous paintings in history. But a closer look reveals something else. In the background is a winding waterway that some scholars believe may be the Arno, the Italian river that flows through Florence and Pisa on its way to the Mediterranean Sea. And while da Vinci was working on the portrait, he also was studying the river to devise an extraordinary plan to change its course.

Da Vinci was not the only Tuscan thinking about the Arno. Niccolò Machiavelli, second chancellor of the Florentine Republic who was later immortalized as the author of The Prince, was also exploring plans to radically alter the river. Their paths would converge in one of the most ambitious engineering schemes of the Renaissance.

Florence's Precarious Position

At the dawn of the 16th century, Florence was a republic in crisis. To the west, Pisa had broken free of Florentine rule and controlled the lower Arno, cutting off Florence’s most direct route to the Mediterranean. Repeated attempts to retake the city had ended in failure. Meanwhile, a new threat emerged to the east. Cesare Borgia, the ambitious son of Pope Alexander VI, was carving out a state in the Romagna.