The Hall at the time of the Sforzas

As emerges from a document dated 2 April 1473, during the rule of Galeazzo Maria Sforza (1466-1476) the Sala delle Asse was lined with wooden planks: a means of insulating the rooms from the cold and the damp. It was in light of this distinctive feature, that Luca Beltrami, the architect who worked on the restoration of the Castle from the late 19th century, renamed the hall the "Sala delle Asse" (hall of wooden boards), the name by which it is still known today.

In 1498 Ludovico il Moro entrusted Leonardo with the painted decorations of the room, as stated in correspondence dated 21 April and 23 April 1498, in which the ducal chancellor Gualtiero Bescapè informed the Duke of Milan that Leonardo was preparing to start work in the “large chamber of wooden boards”, referring to the chamber in the tower.

The De Divina Proporzione, written in 1509 by Luca Pacioli, provides useful clues as to the name of the room and the tree species painted by Leonardo. In the twentieth chapter of the book, Pacioli describes a meeting in the presence of Ludovico il Moro at the castle. In this account he describes the room where the meeting took place as the “room known as the mulberry room”, allowing for the hall to be identified as the very same painted by Leonardo.