Leonardo Da Vinci heavily contributed to Verrocchio's Colleoni equestrian statue monument from both an artistic and structural engineering standpoint. Artistically, his anatomical studies of horses and his notebook entries of the horse's frame by frame movements impacted the Colleoni monument design (Kulenovic and von Platen). In particular, his sketches of the horse's suspended leg and warrior's face are reflected in the monument design. His engineering principles relating to structural stability of the horse with only three ground points are seen through his splitting of the horse into two parts, his idea of removing the inner structure and casting each individual piece into bronze, and the running of a tension bean through the two parts of the horse from the tail to the front of the harness to hold it together (Kulenovic and von Platen). By saving bronze, he saved money and decreased the weight of the horse, which improved stability. The Colleoni monument served as one of the first representations of Da Vinci's ability to combine art and engineering principles.

Sources:

Kulenovic, R., & Von Platen, F. (n.d.). Questions Concerning the Equestrian Statue in Remembrance of the Condottiere Bartolemeo Colleoni in Venice Created in the Workshop of Andrea Del Verrocchio. Retrieved from http://www.museumldv.com/venice.htm