Piero della Francesca (1420 - 1492): Geometric Heads Milan, Biblioteca Ambrosiana, (Source: Pignatti, Terisio, 1982, Master Drawings: From Cave Art to Picasso, Evans Brothers, London, p 17).

Piero della Francesca was a Rennaisance artist who, like da Vinci, worked to produce a mathematically derived system for drawing human proportions which led to a break with the idealised schemas of representation characteristic of earlier european art.