Giotto’s frescoes invite us to ponder the nature of what we instinctively, conveniently, but not very satisfactorily call realism. Compared to the work of his predecessors, these images have a new kind of material presence. Bodies become solid, take on mass and volume, and occupy space. Those in front overlap with and partly occlude our view of those behind, for Giotto wants to set them in the same kind of space that we ourselves dwell in, rather than the immaterial space in which Duccio’s rows of angels can hover one above the other.

There is nothing literally illusionistic in this, nothing that tries to trick us into believing that we are seeing the real world instead of a picture. There is instead an artifice of illusion, a play of conscious reference to natural experience; indeed even in the most overtly naturalistic images, like those of Caravaggio, the effect and the intention are entirely different from the beguiling but superficial conceits of trompe-l’œil.

The purpose of this ‘realism’ is inherently double, or even ambivalent. On the one hand, it is an attempt to give new substance and cogency to the sacred stories. Giotto brings images of faith down from what Yeats called ‘God’s holy fire’ and into the world of human experience. But this is also to accord a new importance to physical and sensorial apprehension; to give the sacred stories new reality by setting them in our world is, implicitly, to modify the standard of reality itself.