The body of man was thought to echo the harmonious form of the universe, and around 1490 Leonardo made a detailed study of human proportion.

He was searching for the ideal form of the body, with each part a simple fraction of the whole – as depicted in his famous drawing of the ‘Vitruvian man’. But when Leonardo actually began to measure a model, he found that the reality was less simple. He was forced to express the proportions in twelfths, seventeenths and so on, and to ‘correct’ his observations to match the theory.

During these years Leonardo was also working on a huge bronze equestrian monument to Francesco Sforza, the former Duke of Milan. To construct the clay model accurately, Leonardo made detailed measurements of several horses. The horse could not be expected to embody any divinely harmonious proportions, and these studies were thus more empirical than Leonardo’s contemporaneous studies of the human form.