There have been many attempts to understand the portrait of the mathematician Luca Pacioli which now hangs in the Museo di Capodimonte, Naples (Plate 1), and which will be familiar to users of the Pacioli 2000 accountancy software. However none of these attempts by art historians engages with the mathematics of the picture, which the artist has gone to such trouble to detail. While to a connoisseur the painting might be thought wooden and peripheral to the history of art, I believe that the artist has recorded the most important meeting of the Renaissance.