One of  the most compelling works of art in Umbria is in the cathedral in Orvieto, and beyond any doubt the greatest achievement of its creator, the south Tuscan painter Luca Signorelli. The Chapel of the Madonna of San Brizio contains his prodigally magnificent fresco  cycle, begun in 1499. Signorelli was hired (after negotiations with Perugino had fallen through) to continue work initiated, or at any rate projected, by Fra Angelico and Benozzo Gozzoli. He was charged with the duty of respecting the conservative tastes of the Orvietans and given a sort of probation before the cathedral authorities allowed him to go ahead with his scheme for decorating the entire chapel for a payment of 575 ducats, a substantial sum in modern terms.

Whatever the scruples of provincial Orvieto, Signorelli set forth on these walls and vaults his own highly idiosyncratic Renaissance vision of a mingled pagan and Christian world, touched by the profound sensibilities of an artist who loved to dress in splendid clothes and who had drawn the body of his dead son so that he might not forget him. Beauty and horror sound here with equal intensity, but each is conceived on an essentially human scale, defined by a series of studies in the nude figure which have no rival until the advent of Michelangelo.

As well as the painted triangles within the vaulting, there are seven frescoes around the doorway, along either wall and flanking the windows behind the altar. Over our heads floats the heavenly company of the Patriarchs, the Doctors of the Church, the Virgins and the Martyrs, picked out against a gold ground in Signorelli’s distinctive pale greens, blues and reds, each a portrait highly individualized in pose and expression. Above the ornately banded arches of the entrance runs an astonishing vision of the end of the world, a wild cosmic anarchy, in which the sea floods the earth and the sun plummets towards a huddle of confused men and women, frightened animals, and an anxious group of prophets (including David and the Sybil) scanning the skies, whence demons hurl their fire at the damned beneath a moon covered in blood.

On the left-hand wall is the figure of the Antichrist, prompted by a devil whispering in his left ear. The false prophet, probably meant to represent Pope Alexander VI (1492-1503), is surrounded by scenes and images of greed, lying and cruelty, while in the background a sinister troop of black-armoured soldiers throngs the portico of the Temple of Jerusalem. Next to this, angles stoop earthwards to crown the elect and summon them to paradise, to the accompaniment of lutes, a harp and a guitar. The left-hand angel stringing a violin is a charming touch.

Here the beauty of the nudes, with their lavishly sculpted contours, is striking enough, but it is in the two frescoes opposite that Signorelli’s true originality as a painter of the human form springs most vividly form the walls. What more hideous than the green buttocks of the grizzled barbarian torturer in The Torments of the Damned, or the monstrous pink sinews toe-nails as he tramples on her head? Could anything, on the other hand, have more grace than The Resurrection of the Flesh, in which we sense all the wonder and astonishment of humanity awakening to new life? In all these works of Signorelli’s there is something deeply un-Italian, a freedom of fancy and a sense of shuddering, diabolical horror which other renaissance painters either shy away from or else do not know. It is sui generis, unique to this visionary master, set apart through his insight into the nature of mortality and the everlasting.

Extracts from Jonathon Keates book on Umbria