The frescoes of the Cappella Nuova in the Cathedral of Orvieto have fascinated visitors from Michelangelo to Freud and Czelaw Milosz because of their dramatic portrayal of the end of the world and the Last Judgment. Creighton Gilbert's study draws on previously overlooked documents to explain the commissioning of this extraordinary cycle of paintings, begun by Fra Angelico in the early 1400s and completed a half-century later by Luca Signorelli...