It is not easy to identify a coordinated vision of Leonardo’s ideal city because of his disordered way of working with notes and sketches. But from the largest collection of Leonardo’s papers ever assembled, a series of innovative thoughts can be reconstructed regarding the foundation of a new city along the Ticino River, which runs from Switzerland into Italy and is 248 kilometres long. He designed the city for the easy transport of goods and clean urban spaces, and he wanted a comfortable and spacious city, with well-ordered streets and architecture. He recommended ‘high, strong walls’, with ‘towers and battlements of all necessary and pleasant beauty’.

His plans for a modem and ‘rational’ city were consistent with Renaissance ideals. But, in keeping with his personality, Leonardo included several innovations in his urban design. Leonardo wanted the city to be built on several levels, linked with vertical outdoor staircases. This design can be seen in some of today’s high-rise buildings but was unconventional at the time. Indeed, this idea of taking full advantage of the interior spaces wasn’t implemented until the 1920s and 1930s, with the birth of the Modernist movement.

While in the upper layers of the city, people could walk undisturbed between elegant palaces and streets, the lower layer was the place for services, trade, transport and industry. But the true originality of Leonardo’s vision was its fusion of architecture and engineering. Leonardo designed extensive hydraulic plants to create artificial canals throughout the city. The canals, regulated by clocks and basins, were supposed to make it easier for boats to navigate inland. Leonardo also thought that the width of the streets ought to match the average height of the adjacent houses: a rule still followed in many contemporary cities across Italy, to allow access to sun and reduce the risk of damage from earthquakes.

Although some of these features existed in Roman cities, before Leonardo’s drawings there had never been a multi-level, compact modem city which was thoroughly technically conceived. Indeed, it wasn’t until the 19th century that some of his ideas were applied. For example, the subdivision of the city by function- with services and infrastructures located in the lower levels and wide and well-ventilated boulevards and walkways above for residents – is an idea that can be found in Georges-Eugene Haussmann’s renovation of Paris under Emperor Napoleon III between 1853 and 1870.

Today, Leonardo’s ideas are not simply valid, they actually suggest a way forward for urban planning. Many scholars think that the compact city, built upwards instead of outwards, integrated with nature (especially water systems), with efficient transport infrastructure, could help modem cities become more efficient and sustainable. This is yet another reason why Leonardo was aligned so closely with modem urban planning and centuries ahead of his time.