From documents now available to us, it is obvious that Leonardo was interested in architecture since his first years in Milan. In the famous 1482 letter to Ludovico Sforza, he in fact describes his competence in military engineering but also adds that in times of peace he believes he can “fully enjoy as much as anyone the architecture, the construction of public and private buildings, and the directing of water from one place to the other;” furthermore, as shown in different pages of the Codex B of the manuscripts in the Institut de France, he studied the issue of Milan’s urban and architectural renewal after the plague that swept over the city in 1484, designing an ideal urban environment: more comfortable, spacious, with well-organized streets and architecture.

He imagined buildings that would distribute water to every room thanks to a mechanical lift system. Furthermore, as we can see in some pages of the Codex Atlanticus, he went so far as to design the model of an ideal city with the perfect integration of a network of canals, used both for commerce and as sewers. The image we gather from his notes is that of a comfortable and spacious city, well organized not only in its streets but also in its buildings, with “tall and powerful walls”, “towers and battlements of necessary and pleasant beauty”, “the sublime magnificence of sacred temples”, and “the convenient composition of private dwellings”.

Leonardo’s city is modern, bourgeois, and rational. It is built on different levels, each independent from the other but communicating with staircases: he thus replicates the social order. At the same time his city is functional: the fruit of the encounter of architecture, mechanical sciences, and hydraulics, it was designed to satisfy the needs of the different social classes. The medieval city layout was certainly a thing of the past, with its narrow streets and overcrowded buildings. However, despite Leonardo’s genius, which could lead him to abandon the ancient city model, his reality was still that exact old urban layout. In the 15th and 16th centuries cities, houses were mostly dark, drinking water came from wells, and rubbish covered most streets – for the most part, they were narrow and unsanitary. It is for this reason that a rational urban layout quickly became the ideal objective of every good governor. Leonardo read and annotated Leon Battista Alberti’s famous treaties, De re edificatoria, but probably it was another volume that especially caught his attention: it is in fact certain he benefited greatly from his personal acquaintance with the Senese Francesco di Giorgio Martini and his writings to better understand the study of statics and the science of construction. Leonardo owned an annotated copy of his Treaty on Military and Civilian Architecture.

Da Vinci’s drawings for the cupola of the Milan Cathedral are also well known, as are the plans for stately homes, for which he designed hanging gardens and innovative interior solutions, such as double and quadruple staircases. Even more interesting are the applications of his talent to the interiors of houses: “with a windmill, I will generate wind in the summer, I will make fresh spring water rise thanks to the use of separate planks […] and more water shall run through the garden, watering the orange and the citron trees according to their need […] thanks to the windmill, I shall also lead many channels of water throughout the house, with sources in different locations, and a passageway with water spouting upward, for whoever may be passing by”.