The Ideal City
After Filarete's project for Sforzinda, an ideal city in honor of Francesco Sforza, Leonardo, as well, was fascinated by the idea of planning a city as a formally complete organism. The waterways are as important as the streets, but
"if you want this to have effect […] you must choose an appropriate site, for example, placing it next to a river that will provide you for canals …"
Milan's problem was the lack of a large river with a constant flow like the Ticino. Leonardo indicated this in his projects, possibly thinking of a new role for Vigevano, a city favored by Ludovico Il Moro.
In order to avoid the violent floods of the river, Leonardo positioned his city at a certain distance and connected it by means of a "larger canal," equipped with a lock:
"when you close the door, the water will fill the lock and the low ships will rise and return to the general level of the city."
The complex network of canals designed by Leonardo provided a transportation system that was independent from the street network. The streets were planned on two levels, each independent from the other.
"Wagons or other similar things ought not to go by the high streets, rather, those should be only for gentlemen; wagons and other loads for the use and convenience of the people ought to go by the low ones. […] Latrines, stalls, and such fetid things as these ought to be emptied onto the subterranean streets."
Because of the plague that infested Milan in 1484, Leonardo gave great importance to cleanliness and hygiene: he projected buildings with porticoes and broad streets where the air could freely circulate, noting
"and further, it would be useful to clean the city frequently […]. And this ought to be done once a year,"
as he was aware of the impact upon Milan when the canals went dry.
Manuscript B, sheet 36 - Manuscript B, sheet 39 - Manuscript B, sheet 47 r.