Sala delle Asse, detail of Monochrome during the restoration (2012-2015)

In a letter dated 21st April 1498, the secretary Gualtiero da Bascapè informed the duke Ludovico maria Sforza called il Moro that Leonardo da Vinci had promised to complete by the following September the decoration of the Sala delle Asse, a large room in the north-east corner of the Castle, at the bottom of the Falconiere tower. Leonardo’s decorative design, on which collaborators may have assisted, was for a great pergola of mulberries, starting from large trees painted along the walls that grew upwards to the vault in a close tangle of branches and golden cords, woven in complicated knots of great elegance. On the room’s northern walls is a large area of preparatory drawing known as the Monochrome, depicting the powerful roots of a mulberry tree working their way into the ground and, with overwhelming strength, breaking up the square-shaped rocks and boulders. This illusionistic composition framed the mouth of the great fireplace that existed in the room in Ludovico il Moro’s day. When the French arrived and the dukedom of Milan was conquered in 1499, Leonardo had to flee the city, probably leaving this work unfinished.
Over the years, the Monochrome shared the fate of the rest of the room’s decoration, being covered over several times with white limewash, often used in the past to disinfect buildings. The polychrome decoration, together with some fragments of the monochrome one, was discovered in the late nineteenth century, during restoration work by Luca Beltrami. Not until restoration work carried out in the 1950s were the plaster layers still covering the Monochrome completely removed revealing this exceptional preparatory drawing which, with its new layout designed by architects’ studio BBPR, was opened for public viewing.
For some time the Monochrome, like the rest of the room’s decoration, had been in a very poor state that not only threatened conservation of the artwork, but also made it difficult to decipher. From 2011, therefore, the 1950s exhibition layout of wooden planks was removed from the walls and an important programme began to investigate and analyse the artwork with a view to better understanding and restoring it, in collaboration with the Opificio delle Pietre Dure (a restoration institute in Florence) and the Ministry of Cultural Heritage. Restoration of the Monochrome was completed in 2015 and, for the international Expo, the room was temporarily reopened to the public.