Which plan did Leonardo da Vinci develop to connect Florence with the sea by water?

To connect Florence with the sea by water, Leonardo da Vinci developed a plan to construct a large canal designed to bypass the unnavigable stretches of the Arno River.1

Building upon a concept that had first been proposed in the 13th century, Leonardo conducted extensive studies of the terrain and riverbank to determine the optimal route. He produced a detailed map illustrating the canal's path, which included a transit through the mountain pass of Serravalle. Although the project was never realized during his lifetime, it remains historically significant because centuries later, the express highway connecting Florence to the sea was constructed along the exact route Leonardo had selected for his canal.1