We are accustomed nowadays to construe pictureplane as picture-space. However, we don’t have to do so, and we were not always so accomplished. It was a geometry of spatial representation invented in the early 15th century, encoding space as plane, that taught us the trick. Before then, picture-plane alone had been able to carry a great burden of religious meaning. Now, within picture-space, theological problem arose. Piero della Francesca was supremely skilled in the application of the geometry. Dr James Lawson, recently retired from the University of Edinburgh, will discuss the procedure, its problems and how Piero addressed them.