Virtual reality systems seek to simulate real scenes so that they will be seen as three-dimensional. The issues at the heart of virtual reality are old ones. Leonardo da Vinci struggled with the differences between the perception of a scene and a painting of it, which he reduced to the differences between binocular and monocular vision. He could not produce on canvas what, in the terminology of Ames, was an equivalent configuration. This was provided 300 years after Leonardo by Wheatstone's stereoscope. Modern approaches to virtual reality that can incorporate moving viewpoints would have fascinated Leonardo.