Piero della Francesca and the Fall of Light on Solid Bodies

The Dream of Constantine 

in The Legend of the True Cross, Basilica of San Francesco, Arezzo

overview of entire choir and its glorious frescoes

The Legend of the True Cross, Piero della Francesca's masterpiece in Arezzo, narrates how, over the centuries, the wood of the apple tree in the Garden of Eden became the cross on which Christ was crucified, through the interventions of the Queen of Sheba, Solomon and the Romans. Later in the story the cross's pedigree is verified and the cross itself plays a role in battles where Christians triumph over pagans. The Annunciation completes the cycle.
For a 3D virtual tour, have a look here.




To place these frescoes* in context: the cycle was painted between 1447 and about 1466; it is preceded by Masaccio's groundbreaking work in the Brancacci Chapel of Santa Maria del Carmine (begun in the 1420s); is contemporary to Gozzoli's Magi Chapel (1459-61) in the Medici-Riccardi palace; and appears a little earlier than Mantegna's Camera degli Sposi in the Ducal Palace in Mantua (1465-74).

But the story and the context are the least of it. What enthuses the modern observer is the extraordinary artistic accomplishment of the entire work: Piero della Francesca's use of perspective, colour, geometry and structure, (not to mention those magnificent, solemn faces and statuesque forms), but also, and what interests me here, his understanding and depiction of light.

a fairly faithful reproduction of the fresco with its faded, cool colouring, perhaps a little less intense than the original although it is hard to say

Most of the scenes in the cycle are bathed in uniform daylight. What galvanizes one's attention on the lower right hand wall beside the window is the bright light, spreading and dipping into shadow, in the scene portraying the dream of the emperor Constantine.

the effect is heightened here by a warm yellow light, not quite true to the original whose colours are cooler

In the dream an angel shows Constantine the cross and a voice says, In hoc signo vinces, 'By this sign shalt thou conquer'. Subsequently, with the cross as his standard, the emperor will conquer his enemies - and eventually convert to Christianity.

The painting features the drastically foreshortened angel plunging down towards Constantine from the top left hand corner of the fresco. Light blazes from the heavenly creature and from the cross he bears, brightly illuminating the tent, Constantine, his sleepy servant and one half of the tent's interior, while strikingly leaving the soldiers' faces and bodies as well as the other half of the interior in true-to-life shadow.

the light/shade contrast is more evident in this black and white detail of the servant

Unlike Masaccio's work in the Brancacci Chapel, where to some extent shadows appear to be created by the light from the central window, this nocturnal or early morning scene is lit by a vividly executed otherworldly glow which displays the artist's awareness of how light falls on solid bodies, and how to represent the phenomenon pictorially. 
This attempt is exceptional in the art of Piero della Francesca's day. Caravaggio would not paint his striking night scenes  for another 150 odd years.

Caravaggio's The Taking of Christ, 1602, National Gallery of Ireland, Dublin

Piero della Francesca was the author of treatises, De Prospectiva Pingendi (On the Perspective of Painting) and and De Quinque Corporibus Regularibus (Of the Five Regular Bodies), on arithmetic, algebra, geometry, solid geometry and perspective. Influenced by Alberti's De Pictura, he was however less theoretical and general in his attempt to furnish practical, specific applications for artists. How to represent 'light falling on solid bodies' was consequently of great interest to him and the technique is clearly being explored in this breathtaking work.

from De Prospectiva Pingendi an interesting study of a form closely resembling Constantine's tent

detail, Madonna and Child with Saints, 1472-1474, Pinacoteca di Brera, Milan

  






Post Scriptum:
A curious detail which emerged after restoration of the Constantine fresco is the presence of stars in the night sky above Constantine's camp. It appears that Piero della Francesca portrayed some actual constellations in this patch of sky. The Little Dipper (Ursa Minor) with the North Star at the end of its handle, has been identified, as have Cassiopeia, the Pleiades, Aldebaran and others. Strangely, their actual positions are inverted. This is apparently owing to Piero's use of a sky map or globe for his painting, for these tools typically furnished a mirror image of the constellations.**

*In fact these paintings use a mixed technique of fresco, tempera (egg tempera) and tempera grassa (egg tempera with oil) and recently it has been discovered that Piero's Resurrection, a far smaller work, also used a mixed technique

**For more information, see an article by Vladimiro Valerio.