Foreshortening is the perspectival technique of depicting objects, bodies or architectural elements at extreme angles to the picture plane, so that they appear to recede strongly in space. It requires calculating how much a form must be compressed in the picture to simulate the visual shortening that the eye perceives when an object is directed toward or away from the viewer. Andrea Mantegna's Lamentation over the Dead Christ (c.1480) is the canonical example: the dead Christ lies feet-first toward the viewer, dramatically compressed along the picture plane, in a perspective so radical it is almost disturbing. Michelangelo's Sistine Chapel ceiling uses foreshortening throughout to create the illusion that figures overhead occupy real space. The technique requires mastery of perspective, anatomy and the mathematics of projection.