From 1484 to 1485, the Black Death swept through Milan, where Leonardo was living at the time. Several outbreaks occurred in a short period of time. The narrow and crowded city streets helped with the spread of disease, and in the end, about one third of Milan's population had been killed. It was this devastation that inspired da Vinci to make plans for a better city, and ideal city. Leonardo worked for several years to perfect the designs. The ideal city would have two levels. The lower level would feature a series of canals to be used for transportation of people & goods, it would also be used as a sewage system. The upper level would be the picturesque part of the city, with wide roads and extravagant buildings. Tradesmen and lower class workers would travel on the bottom level, while higher class gentlemen would be on the top roads. Though da Vinci's plans were a detailed and well thought out design for a more sanitary city, they were never put to use, as it would have required a complete rebuild of the city.

Sources: https://www.fastcompany.com/90163788/the-plague-inspired-da-vinci-to-design-a-city-we-should-steal-his-ideas

http://www.da-vinci-inventions.com/ideal-city.aspx

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