If one had to choose a characteristic of Italian art that sets the 15th century apart from previous periods, it could only be perspective. The depiction of three-dimensional forms on a two-dimensional surface as theorized by Brunelleschi and mathematician Luca Pacioli was as powerful then as the advent of virtual reality is today. Perspective made it possible for artists to render a scene with dramatic realism, and to open up a surface, allowing the eye to gaze towards infinity and imagine that the wall or canvas were not there.
Perspective would be brought to the height of illusion only later, in 17th century Baroque painting, with massive architectural scenes rising vertiginously towards the heavens, as in Andrea Pozzo’s fresco in the church of Sant’Ignazio, Rome. Leonardo da Vinci had already experimented with this technique in his Last Supper in Milan, in which he places the scene in a space whose perfect perspective makes it a visual extension of the room. But there is another less familiar fresco in Milan, painted by Leonardo and his assistants in about 1498, that shows that the artist was, differently to many other painters of his generation, in no way a slave to the enticing possibilities of linear perspective.
The unfamiliarity of the Sala delle Asse at the Castello Sforzesco is due to the fact that it was forgotten for four hundred years, from when the city of Milan was conquered by France – after which the fresco was covered in plaster and the hall converted into stables – until the late 19th century, when it was revealed during restoration. The work was attributed to Leonardo only in the 1930s, on the basis of documents concerning the commission from Duke Ludovico Sforza.
But it is an exceptional work. Leonardo’s concept for this square-plan hall in the north tower of the castle was to paint a scene that negated the existence of the walls and ceiling, not by means of trompe l’oeil architecture, but by natural elements alone – trees and foliage. The entire ceiling is covered by an intricate pattern of branches and leaves, supported by a series of massive tree-trunks all around the walls. Sadly the painting is not in good condition. The colours are marred by the whitish saltpetre that often crystallises on the surface of frescoes, and most of the lower section has completely disappeared. Nonetheless, one can appreciate the visual effect of the work, with the blue sky filtering through the meticulously-painted greenery.
Leonardo da Vinci had to work with the existing structure of the room, which has a series of pedentives running around the base of the ceiling vault, and he invented a typically brilliant solution. Instead of painting “natural” trees, he envisaged a pattern of branches that are tied into shape by means of a series of ribbons, so that the branches follow the pattern of the arches. In this way the three-dimensionality of the scene becomes more believable.
The remarkable feature of the painting is the fact that Leonardo da Vinci has attempted to portray the view into space, towards infinity, using no elements of perspective at all, with just the contrast between the trees and foliage and the sky beyond. The painting therefore becomes an example of natural perspective. Leonardo was in fact the first person to make the distinction between “synthetic perspective”, the geometrical form of perspective based on a single vanishing point, and “natural perspective”, based on the complex interactions between the perceived world, with its multiple vanishing points and spherical geometry, and the human eye in perpetual movement.
The only section of the lower section of the fresco that has survived demonstrates the fact that Leonardo deliberately wished to work without linear perspective. The trees are shown as growing from a series of stratified rocks, so that the observer is placed inside a sort of depression inside a rock-lined space, which effectively eliminates the horizon.
It may also be that Leonardo intended to add the dimension of time to this spatial composition. One has the impression that the trees are growing from ancient ruins, as if the fresco anticipates the scene as it may be aeons in the future, when the castle itself has collapsed and nature has reclaimed the area. Certainly, this fresco, like all Leonardo’s works, conceals an extraordinary depth of intellectual study, and it is a worthy counterpart to the Last Supper in the same city.