Was it the vicious attack on the 'obscenity' of his Sistine Chapel nudes (by a pornographer) that sent Michelangelo in a different direction in his last paintings? Andrew Graham-Dixon penetrates the Pauline Chapel at the heart of the Vatican to find a terrible vision of grace - and art - renounced
In November 1545, having unsuccessfully attempted to blackmail Michelangelo into giving him some drawings, the courtier, art dealer, poet and pornographer Pietro Aretino set out to take his revenge on the most celebrated artist in Italy. Aretino composed an ornate, venomous open letter to Michelangelo - "one of the nastiest letters ever written" was how the art historian Linda Murray once described it - in which he reproved him for the profusion of nude figures in his recently completed fresco on the altar wall of the Sistine Chapel, The Last Judgement. After paying several double-edged and thoroughly insincere compliments to "the divine Michelangelo", Aretino wrote:

"On seeing ... the whole of your Day of Judgment, I was able to perceive

the noble grace of Raphael in the lovely beauty of its invention. Nevertheless I, as one baptised, am ashamed of the licence, so harmful to the spirit, which you have adopted ... Is it possible that you, who as a divine being do not condescend to the society of men, should have done such a thing in the foremost temple of God? In the most important chapel in the world, where the great cardinals of the Church, where the reverend priests, where the Vicar of Christ with Catholic devotions, with sacred rites, and with holy prayers, bear witness to, contemplate, and adore His body, His blood, and His flesh? ... What you have done would be appropriate in a voluptuous whorehouse, not in a supreme choir."

This was by no means the first criticism to have been levelled at the artist's religious works on the basis of their presumed obscenity, although it was certainly the most absurd - the nakedness of the figures in The Last Judgment is not in the least lubricious but signifies the nakedness of all mankind in the eyes of God - and it proved, eventually, to be among the most telling. In 1519, the dour and ill-fated Dutch pope, Hadrian VI, had taken one look at Michelangelo's earlier and yet more celebrated cycle of frescoes, on the ceiling of the Sistine Chapel, and dismissed it as "a brothel". But Hadrian had been out of joint with his times and when he was found dead, presumed poisoned, just a few months into his papacy, that remark was soon forgotten.

Aretino's calculated attack of the mid-1540s, on the other hand, was a very different matter. He was giving voice to sentiments that, as he well knew, were shared at that period - which coincided with the first true stirring of the Counter-Reformation - by many members of an increasingly severe and censorious Roman clergy. The Church eventually acted on his criticisms of The Last Judgment, waiting tactfully until Michelangelo's death in 1564 and then promptly employing the artist's former friend Daniele da Volterra - subsequently nicknamed Il Braghettone, "The Breeches-Maker" - to paint draperies on to the offending nudes. Thus it was that Pietro Aretino, author of sundry erotic works including the notorious Tales of Nuns, Wives and Courtesans - in the first chapter of which several nuns sodomise one another with leather dildos - became self-appointed censor- in-chief to the Vatican.

The censors and inquisitors of the Counter-Reformation have long departed. These days the knowledge that The Last Judgment could once have been made to seem shocking seems itself mildly shocking. It is patently such a severe and recriminatory picture, a graphically harsh reminder of the ultimate consequences of sin. Now, in the Sistine Chapel, it is chiefly tourists who come and go, talking of Michelangelo - until they are silenced by the ever-present admonitory shushing guards, who are employed by the Vatican Museums to enforce a virtually Trappist reverence before the works of divinely inspired genius. Approximately 2.5 million tourists came and went last year, at a rate of around 8,000 a day, and sales of the illustrated guidebook, Michelangelo in the Vatican (Edizioni Musei Vaticani), were brisk. Statistically speaking, that makes Michelangelo one of the most popular painters in the world. But by comparison with other conspicuously popular painters, notably Vincent Van Gogh, he is widely regarded as a remote, obscure, somewhat impersonal figure: a landmark, a phenomenon, rather than a mere man. In fact, his art speaks at least as directly as that of Van Gogh about his emotions, his desires and spiritual yearnings. It is shot through with evidence of his own personal compulsions. But despite that - and despite Charlton Heston's exaggeratedly manful if somewhat misguided attempts to bring the artist to life in the Hollywood version of Irving Stone's The Agony and the Ecstasy - as far as the layman is concerned, no great cult of personality attaches to Michelangelo's name. Awe rather than sympathy is perhaps the commonest response to his achievements.

This might begin to change were the Vatican to open one of its better- kept secrets to the public. Just beyond the Sistine Chapel, through a pair of tall, locked double doors patrolled by Swiss Guards, lies the Pauline Chapel; and within the Pauline Chapel are to be found Michelangelo's last and most overtly autobiographical paintings. Because this particular chapel has always been reserved for the private use of the Pope, only exceptionally persistent or fortunate applicants to the Vatican ever get to see them. Unlike the Sistine Chapel paintings, they remain unrestored, although conservation is currently under discussion and it seems that future public display is not inconceivable. After the frescoes illustrating scenes from the Old Testament on the Sistine ceiling, completed in 1512, and The Last Judgment, completed in 1541, they, represent the third and final act of Michelangelo's career as a painter - and, indeed, they look like paintings that were meant, quite deliberately, as a kind of full- stop.

The Pauline Chapel paintings were commissioned by Pope Paul III - after whom the chapel was named - in 1542. Michelangelo, who was by then almost 70 years old and could no longer work as quickly as he had in his youth, was in the middle of painting them when he received Pietro Aretino's malicious open letter of November 1545. The artist never even bothered to answer the letter, although his attitude to the strain of criticism that it epitomised is fairly clear from his later response to a papal request that he "amend" The Last Judgment. "Tell his Holiness," Michelangelo said to the Cardinal who had brought the message, "that it is only a small matter, and when he has made the world a better place, pictures will amend themselves."

Compared to the Sistine Chapel, the Pope's private chapel is an intimate space, a barrel-vaulted basilica not much longer than a cricket pitch, which must have been much plainer in Michelangelo's day than it is now - a polychrome Baroque altar and elaborate stucco ceiling decorations were added in the 17th and 18th centuries. The two great Pauline Chapel frescoes jar with these later additions, which look like somewhat half- hearted attempts to soften the impact of Michelangelo's terribilita. If that is so, they did not succeed. Each picture dominates the side wall it decorates, so anyone who would wish to penetrate to the heart of the chapel - this has most often meant the Pope himself - must first run the gauntlet of Michelangelo's solemn, spiritually accusatory imaginings.

The first fresco he completed is to the left as one enters. Its subject is The Conversion of Saul on the Road to Damascus. The story comes from Acts and tells of the moment when Saul of Tarsus, an impious lawyer and persecutor of Christians, was suddenly converted by an act of God:

"This is what happened. I was on the road and nearing Damascus, when suddenly about midday a great light flashed from the sky all around me, and I fell to the ground. Then I heard a voice saying to me, 'Saul, Saul, why do you persecute me?' I answered, 'Tell me, Lord, who you are.' 'I am Jesus of Nazareth,' he said, 'whom you are persecuting.' My companions saw the light, but did not hear the voice that spoke to me. 'What shall I do, Lord?' I said, and the Lord replied, 'Get up and continue your journey to Damascus; there you will be told of all the tasks that are laid upon you.' As I had been blinded by the brilliance of the light, my companions led me by the hand, and so I came to Damascus."

The uncommon theme of Saul becoming Paul may have been suggested by Pope Paul III, who showed a special devotion to the feast of his namesake's conversion. If so, Michelangelo made the subject entirely his own. He treated it in an unprecedented way, showing a thorough disdain for harmonies of composition or indeed any other merely aesthetic grace.

Above, Christ descends from the heavens like an avenging angel and casts a thunderbolt with his right hand. Beneath, on the ground, Saul lies struck down and temporarily blinded, while his bolting horse rears and his attendants scatter. The initial impression is one of great busyness, of a momentous event taking place amid obscuring crowds of ancillary figures. The sky is thick with Christ's heavenly host and the earth is congested by Saul's fleeing followers. But Michelangelo is patently uninterested in the large majority of the figures that staff the scene. His attention is so exclusively focused on the relationship between the all-powerful Saviour and the stunned Saul, that he has made all the rest seem to fly off like chaff in the wind. Christ above is the middle of a centrifuge, a still point of authority from which his attendant angels seem to spin away - an effect enhanced by the curious disjointed groupings Michelangelo devised for the heavenly host, making them look like the broken pieces of a jigsaw puzzle - while Saul's stocky but inelegant followers are almost all running away, as if trying their best to get out of a picture that has no place for them.

Michelangelo is renouncing his own fabled ability - exuberantly demonstrated in the Sistine Chapel ceiling and less certainly in The Last Judgment - to orchestrate a huge number of figures within the compass of a single composition. The Conversion of Saul is the pictorial equivalent of a discord. The effect is one of grim self-parody, of a painter going through the motions of a virtuosity that he has come to despise in himself.

The painting is not a success, exactly, but it is powerfully expressive of the artist's changed priorities in the last decades of his life. The Last Judgment - and this must have made the criticisms levelled at it all the more painful to Michelangelo - had marked an earlier stage in the artist's poignant struggle to rid himself of his attachment to a sensual dream of beauty. In the Pauline Chapel frescoes, that struggle has been finally resolved. Here Michelangelo is no longer a Renaissance man, in the sense that the desire to compete with the art of ancient Greece and Rome has ceased to motivate him. There are, admittedly, echoes of antiquity in the painting - the prone figure of Saul is in the pose of a Roman river god, while the man restraining the bolting charger echoes the famous Horse Tamers of the Quirinale - but these are faint and absent-minded recollections of a Greco-Roman world which, in his old age, no longer meant what it had once meant to Michelangelo.

There is no joy, no sensuality or energy in the figures in The Conversion of Saul. They are heavy, flat-footed, thick-waisted. The art historian Sydney Freedberg wrote well of these frescoes: "The human body is the earthen shell, the carcer terreno of a spirit that seems not to possess a private will or even specified identity. This is an abjuring of a whole life's history, and of the aspirations of the time in which it had been made: in the deepest possible sense an anti-classicism, and a negation of the Renaissance."

The artist seems not to want to paint like himself any more, and behind the ponderous, gravity-bound figure style of his last paintings, there may lurk the ghost of Giotto, the most celebrated Italian painter of the 14th century. Announcing the end of the Renaissance, Michelangelo reverts to a style that predates it, as if by reviving a brusquer and less polished manner he might convey - and encourage - a simpler and more direct belief in God. All that matters, Michelangelo now declares, is blind faith, and the only parts of the painting to have been handled with true conviction are the two figures who communicate the spiritual heart of its message: Christ above (whose striking pose, airborne and dynamic, much impressed the young Tintoretto) and Saul down below, whose eyes are closed and whose pained but rapt expression speaks of private communion with God. Michelangelo painted Saul not as a young man, as he is in the Bible, but old and grey. It is possible that the artist intended the figure as a kind of self-portrait. If so, it would not have been the first time that he had included himself in his work. He had painted his own features into The Last Judgment, too, where his is the face grotesquely folded in on itself in the flayed human hide carried by St Bartholomew.

Giorgio Vasari, who knew Michelangelo well, left a memorable description of the artist in his old age, ascetic and evidently somewhat indifferent to appearances:

"Michelangelo's constitution was very sound, for he was lean and sinewy... he could always endure any fatigue and had no infirmity, save that in his old age he suffered from dysuria and gravel... As he grew old he took to wearing buskins of dogskin on his legs, next to the skin; he went for months at a time without taking them off, then when he removed the buskins often his skin came off as well ... His face was round, the brow square and lofty, furrowed by seven straight lines, and the temples projected considerably beyond the ears, which were rather large and prominent. His body was in proportion to the face, or perhaps rather large; his nose was somewhat squashed, having been broken... his eyes can best be described as being small, the colour of horn, flecked with bluish and yellowish spark. His eyebrows were sparse, his lips thin (the lower lip being thicker and projecting a little), the chin well formed and well proportioned with the rest, his hair black, but streaked with many white hairs and worn fairly short, as was his beard, which was forked and not very thick."

The second picture the old man in the dirty buskins painted for the Pauline Chapel is yet more intimidating and impressive than the first. A solemn, baleful work, it sticks in the memory like a fishbone in the throat. Its subject - again an unusual one - is The Crucifixion of St Peter. On a barren hillside, a crowd has gathered to witness the martyrdom of Peter, who has been nailed to a cross, which is being lifted into position by a gang of burly Roman soldiers. According to the biblical apocrypha, Peter insisted on being crucified upside down, and that is how we see him - except that he is the one looking at us. He has raised himself up and wheels round awkwardly on the instrument of his torture to stare us in the eye. His torturers seem not actively malicious but passive, hypnotised, like sleepwalkers acting out a compulsion (it has been suggested that Michelangelo was influenced by Martin Luther's severe doctrine of predestination). All is terror and stunned silence. The grim face of Peter is overpoweringly urgent, nailing you to the spot as surely as the saint's feet are nailed to the heavy cross of blond wood. It is difficult to think of any other picture, anywhere in the world, in which the protagonist looks you in the face and will not let go quite like this. All the other figures are ghosts, the soldiers arriving in an irrelevant clamour in the upper left- hand corner epitomising the irrelevance of human history itself - a busy but pointless march of mundane events across the field of the world - to Michelangelo's vision of things at this point in his life.

Peter, the Rock on whom Christ built his Church, symbolised the papacy, but Michelangelo's picture goes beyond papal propaganda. It looks more like a reminder to the Popes of their own responsibilities, placed at the heart of the Vatican by a man who had worked for the papacy - and had seen the foibles and frailties of living Popes at first hand - for more than 50 years. Many, many years before, Pope Leo X had confided to the painter Sebastiano del Piombo that "Michelangelo is terrible; one cannot deal with him". Morally, in the Pauline Chapel, the artist sets himself above his patron. Arrogance was perhaps the one characteristic of his youth that the artist never entirely outgrew. St Peter, like Saul in the fresco opposite, is almost certainly an idealised self-portrait. Looking at the picture is eerie, like suddenly coming face to face with suffering, old, devout, fiery Michelangelo himself.

Not long after he finished The Crucifixion of St Peter, the artist wrote one of his most moving sonnets, a poem in which he announces the end of his life and renounces art. The best modern translation (by Creighton Gilbert) runs as follows:

"My course of life already has attained,

Through stormy seas, and in a flimsy vessel,

The common port, at which we land to tell

All conduct's cause and warrant, good or bad,

So that the passionate fantasy, which made

Of art a monarch for me and an idol,

Was laden down with sin, now I know well,

Like what all men against their will desired.

What will become, now, of my amorous thoughts,

Once gay and vain, as towards two deaths I move,

One known for sure, the other ominous?

There's no painting or sculpture now that quiet

The soul that's pointed toward that holy Love

That on the cross opened its arms to take us."

When Michelangelo painted his last pictures he was in no need of advice from Counter-Reforming clerics (or pornographers); for he was, himself, in the middle of his own personal Counter-Reformation - rejecting the tremendous sophistication and grace of his earlier works; turning his back on the passion and love he had once brought to the depiction of the male nude; creating an art that spoke of its creator's disillusionment with art itself, and his readiness for the beyond. In the Pauline Chapel, Michelangelo snapped his wand