all its parts, another model was begun because Da Vinci would fain show the warrior triumphing over a fallen foe.[249] The first motive seemed to him tame; the second was unrealisable in bronze. "I can do anything possible to man," he wrote to Lodovico Sforza, "and as well as any living artist either in sculpture or painting." But he would do nothing as taskwork, and his creative brain loved better to invent than to execute.[250] "Of a truth," continues his biographer, "there is good reason to believe that the very greatness of his most exalted mind, aiming at more than could be effected, was itself an impediment; perpetually seeking to add excellence to excellence and perfection to perfection. This was without doubt the true hindrance, so that, as our Petrarch has it, the work was retarded by desire." At the close of that cynical and positive century, the spirit whereof was so well expressed by Cosimo de' Medici,[251] Lionardo set before himself aims infinite instead of finite. His designs of wings to fly with symbolise his whole endeavour. He believed in solving the insoluble; and nature had so richly dowered him in the very dawntime of discovery, that he was almost justified in this delusion. Having caught the Proteus of the world, he tried to grasp him; but the god changed shape beneath his touch. Having surprised Silenus asleep, he begged from him a song; but the song Silenus sang was so marvellous in its variety, so subtle in its modulations, that Lionardo could do no more than recall scattered phrases. His Proteus was the spirit of the Renaissance. The Silenus from whom he forced the song was the double nature of man and of the world.