Leonardo seems to have become a prominent figure in Sforza's court fairly soon after his arrival in Milan. During the 1480s, he worked on two famous portraits, the Portrait of a Musician and the Lady with an Ermine. He also began work on the bronze horse. Sforza, who was not the legitimate ruler of Milan, was eager to erect monuments that would remind the town of his heritage and authority: the large equestrian statue was to honor his father. Leonardo planned a horse that would stand twenty feet tall and comprise 200,000 pounds of bronze. Never had a bronze statue approached this size, and Leonardo never had the chance to cast it, though he continued to work on different designs, molds, and models throughout the 1880s and 1890s. The project took up a great deal of his time, and was one of his greatest failures. When the French invaded Milan in 1499, idle archers used the model of the horse for crossbow practice.
The pattern of work that we see Leonardo developing in Milan would come to persist throughout his life: while conducting intense scientific investigations in his spare time, the artist would work on one or two major public projects (such as a monument or mural), doing a few portraits on the side.