"Predella Panel, The Pisa Altarpiece"

The scene on the left demonstrates Masaccio's skilful use of linear perspective, right down to the foreshortening of the halo of St Peter. The action appears to take place in a space behind the picture plane, and the figures within this space appear as solid three-dimensional objects. The two men on either side of St Peter appear to lean forward in space, out towards the viewer, as they hammer in the nails on the cross.