Leonardo never had the opportunity to test his casting system: in 1494 the invasion of Italy by Charles VIII of France prompted Ludovico il Moro to dispatch the bronze originally intended for the monument to the Duke of Ferrara, Ercole I d'Este, for casting artillery instead. From this moment on, the project remained on hold.
Political and military events – culminating in the French occupation of Milan in 1499 and the subsequent fall of the Sforzas – sadly prevented the completion of the project. Leonardo was never able to test his casting process. On 9-10 September 1499, French troops led by Marshall Gian Giacomo Trivulzio burst into Milan and destroyed the clay colossus. It may have been moved from the Corte Vecchia workshop to land owned by Leonardo near S. Vittore al Corpo Monastery, where the foundry was presumably installed.
Having worked for more than sixteen years on the development of the casting method and the construction of the moulds, Leonardo was forced to abandon the project.
This is the last reference to Leonardo's colossus. Some years later, in 1508, Leonardo was engaged in the project of another equestrian monument for the Maresciallo Trivulzio. We know from the only extant technical manuscript that he had planned the same casting process conceived for the Sforza horse. However, in this case too, the bronze sculpture was never cast.