Who can look at Bernini's Ecstasy Of St Theresa (1644- 47) with an innocent eye? On a scalding Roman summer afternoon some years ago, a trio of sandalled nuns came into the dark church of Santa Maria della Vittoria and approached the Cornaro Chapel. I was sitting in one of the pews opposite, unsettled as usual by what I was seeing - intermittently illuminated rapture. Every so often a coin would clunk into the pay-for-light box, and the most astounding peep show in art would proceed: the saint's head thrown back, her mouth, its upper lip drawn back, opened in a moan, heavy-lidded eyes half-closed, shoulders hunched forward in both recoil and craving. Beside her, a smiling seraph delicately uncovers Theresa's breast to ease the path of his arrow.
The nuns stayed for 10 minutes, stock still, then two of them genuflected, crossed themselves, as well they might, and left. The third sister sat down in another pew, dipped her head in prayer and occasionally caught my eye as I tried not to wonder what she was thinking and feeling. Bernini's sculpture is, after all, a spectacle that hovers on the borderline between sacred mystery and indecency. Scholars have fallen over themselves to warn us that what we are looking at could not possibly be a moment of sensual surrender. It is utterly unhistorical, these interpreters insist, to imagine the Pope's architect could conceive of representing the mystical levitation of a saint as a moment of orgasmic convulsion. But as a matter of fact, the modern anachronism is not the union of body and soul that so many 17th-century poets and writers obsessed about, but its demure separation into sensual and spiritual experience. Ecstasy in Bernini's time was understood, and experienced, as sensuously indivisible.
A century after he had made this most miraculous and emotionally overpowering of all his works, a French aristocratic connoisseur, the Chevalier de Brosses, passing through Rome on the Grand Tour, took one look at the saint and made a remark that has become infamous for its smirking cynicism: "Well, if that's divine love, I know all about it." But the Chevalier may have understood more than he affected to know: that the intensity of Theresa's ecstasy, the representation of the transport of the soul, in fact, had everything to do with carnal knowledge, especially Bernini's own.
Before Bernini, sculpture's preoccupation had been with immortality. When modern sculptors looked at, and learned from, antiquity, what they saw was the translation of mortal humanity into something purer, chillier and more enduring: gods and heroes. Michelangelo's self-appointed mission, famously, was to tease out from the marble those ideal forms he believed lay trapped within it. So the heroic power of his David (1504) lies precisely in its inhumanly frozen immobility. Michelangelo was not much interested in the rendering of common bodies, still less in the imitation of workaday faces. His passion was to approximate men to gods. So no matter how grand the subjects - Pope Julius II, for example - he never bothered with so much as a sitting.
Gianlorenzo Bernini, on the other hand, cared a great deal about likeness, to the point where he redefined it as more than appearance. True likeness - the kind he wanted to capture in his sculptures - was the animation of character, expressed in the movements of bodies and faces. Bernini took the stat - the Latin for their usual condition of "standing" - out of statues. His figures break free from the gravity pull of the pedestal to run, twist, whirl, pant, scream, bark or arch themselves in spasms of intense sensation. Bernini could make marble do things it had never done before. His figures charge into hectic action. Most of them are naturally yeasty, on the rise, and their natural drift is into the air and light. So on Rome's Ponte Sant'Angelo, Bernini's angels trip into the sunlight. Within the basilica, his bronze columns supporting the canopy - the baldacchino - over St Peter's tomb aren't static; they writhe and seethe with organic life, bees and leaves teeming on their surface. Beyond the baldacchino, at the farthest end of the basilica, the Cathedra Petri - the throne of St Peter himself, the seat on which the entire Church of Rome institutionally rests - is held aloft on the fingertips of the apostles, as though it were a holy Lilo bobbing on a cushion of celestial helium.
It's magic. And that was precisely why, after his death, Bernini would be attacked by artists such as Sir Joshua Reynolds for being a cheap sorcerer, a specialist in theatrical trickery, who - for the sake of wowing the worshipper - had, unlike Michelangelo, debased the purity of his chosen material. The two classicist gripes against the Baroque Bernini were that he was emotionally overloaded and that by going to such great lengths to imitate the surfaces and textures of other materials - steel, fur, skin - he had betrayed the integrity of stone. The more he made marble impersonate some other substance, the critics complained, the farther from the sublime he took the beholder and dragged him down to earth.
According to the contemporary writer Filippo Baldinucci, Bernini liked to boast that in his hands marble could become as impressionable as wax and as soft as dough. Bernini's marble does indeed seem to mutate into other substances: fibrous rope; brilliant steel; locks of hair. Through understanding the way light could strike a highly polished surface, and how deep incising with a fine drill-head could supply shadow, he could even make the skin of a figure appear to sweat. All of this made him an exceptional dramatist, and just as his talent as a painter played into the colour that we imaginatively sense in his stone figures, so his third career as writer, producer and actor of Roman plays meant he was committed to sculpture as a high performance art.
Contemporaries marvelled at this virtuosity, and believed that Bernini's unearthly powers as the Great Transubstantiator were a sign that he must have been kissed by God. False modesty was definitely not one of his failings. But since there had never been a time when he had not been hailed as a human marvel, it's surprising he wasn't more swollen-headed. The child Gianlorenzo, paraded and promoted by his father, was singled out as extraordinary. Brought before the Borghese Pope Paul V, the eight-year-old did a shrewdly ingratiating lightning sketch of Saint Paul "with free bold strokes" that moved the astonished Pope to hope that he was looking at the next Michelangelo. To nurture his talent, Paul V appointed Cardinal Maffeo Barberini to watch over the young Bernini and shape his education.
Years of what all sculptors had to do - study and draw from classical models - followed. Even boy wonders had to learn the rules. But Bernini was later famous for saying that "those who never dare to break the rules never surpass them", and there was something else apart from antique busts and torsos that he was evidently looking hard at - himself. For all three of the great masters of 17th-century dramatised realism - Caravaggio, Rembrandt and Bernini - the mirror was almost as important a tool of their work as the brush, etcher's needle or chisel.
Bernini was only 15 when he made his first experiment in this ego-play, The Martyrdom Of San Lorenzo (1613). St Lawrence was the librarian and archivist of the early Church, who had been roasted alive on a red-hot griddle. Since the saint was Bernini's namesake, the project was personal, but he took this identification to extremes by placing his own leg against the side of a hot brazier. Either he looked in a mirror while he was performing this exercise in tutelary masochism, or he had someone hold it as he sketched the expression of pain on his own face. But the look of St Lawrence is a peculiar mix of agony and ecstasy, because Bernini is trying to catch a literal turning point in the story of the martyrdom. According to popular hagiographies, at the height of his suffering Lawrence turned to his tormentors and told them, since one side was done, to turn him over. No wonder he became the patron saint of cooks.
That moment is not just one of macabre drollery, but one of profound alteration. For as St Lawrence went on cooking, so the legend had it, the smell of scorching human flesh turned, miraculously, into the most intensely sweet fragrance. Brutish nostrils quivered; incredulous pagans were converted; souls were saved. It's this precise moment of transformation, at once spiritual and carnal, that Bernini tries to seize, and that he would repeat 30 years later in The Ecstasy Of St Theresa. Fire, the natural medium of the sanguine humour (which was certainly Bernini's), played a critical role in both pieces. That had been the element that champions of painting's superiority over sculpture had bragged could never be reproduced in stone, which is why the teenage Bernini went to such lengths to render the licking flames so realistically that the coals seem in our mind's eye to glow red.
How could the cardinals not notice such a prodigy and compete for his services? As Rome under the popes of the Baroque age became more aggressively confident, with new churches being built and old ones renovated, the authority and power of the cardinals rose along with that of the papacy. They swaggered for Christ. And they needed a brilliant stable of artists to help them do the swaggering.
Up on the Pincian Hill above the Piazza del Popolo, Cardinal Scipione Borghese was building a spectacular villa, in conscious competition with the Palazzo Barberini. Marble halls would house a collection of antiquities, but the ancients were to be complemented by the moderns. So the cardinal, who had certainly seen the fountain statuary Bernini had created for Cardinal Montalto - a furious Neptune ploughing the waves with his trident as though spearing sharks for dinner - wanted to grab the 20-year-old genius for his own. Bernini repaid this vote of confidence with a procession of dumbfounding masterpieces - The Rape Of Proserpine (1621-22); Apollo And Daphne (1622-24); and David (1623-24), for which he once again used his own face and body as model.
Michelangelo's David seems to be gathering all his powers for the combat; Bernini's David is at the point of discharging it. The veins in his arm protrude through his skin with the muscular effort. He pivots on the ball of his foot almost like a discus thrower, his left heel raised to apply more spinning force. The face of Michelangelo's hero is impassively beautiful, but Bernini's works: brows furrowed, jaws clenched, lips pursed. And those features are so precisely registered because, of course, they are Bernini's own, seen in a mirror held for him, according to Baldinucci, by Barberini himself.
As with Caravaggio, there's never a time when Bernini isn't conscious of the spectator, moving around the piece and seeing it work in different ways from different perspectives (even when, as seems to be the case, its back was originally against the wall of the room). Centuries on, this understanding of sculpture as presenting not one but multiple images to us, each in a state of mutating motion as we move about it, might seem a truism; but in the 1620s it broke all previous conventions. Bernini had discovered a way to make marble movies.
And the violent onrush of action, which in David just implies another figure - Goliath - turns into actual collisions in the two great mythological pieces that made his fame: The Rape Of Proserpine and Apollo And Daphne. Against the odds, Proserpine does what she can to counter her attacker, Pluto, and the sexual equalisation goes a stage further with Apollo and Daphne. Apollo may be modelled on the acme of beauty-made-visible, but his prey still eludes him. Even more than in the David, this is a frozen split second; Apollo is thwarted by a lightning metamorphosis as Daphne's body seems to climb into the sky like the tree she is instantly becoming.
So we are witnessing two marvels: the transformation of fingers into sprouting twigs, with the tips of the nymph's toes rooting in the soil, and the stupendous capacity of the sculptor to render the nanosecond with such material vividness. At several cunningly calculated points, it is not clear where Apollo ends and Daphne begins. Her spray of laurel (the trophy of victors) that sprouts against Apollo's barely covered groin acts as a sign of his sexual urgency and so magnifies the drama of his frustration.
Barberini, who was rapidly becoming Scipione's rival as friend and patron, felt obliged to add a ploddingly moralising couplet in stone at the foot of the sculpture lest people get the wrong idea: "The lover who would fleeting beauty follow, Plucks bitter berries, and leaves his hands hollow."
When, in 1623, Barberini became Pope Urban VIII, he pounced and, unlike Apollo, got his way. Bernini was called into the papal apartments; what Urban VIII had in mind for the Cavaliere (for Bernini had been knighted in the Order of Christ by Urban's predecessor, Gregory XV) was nothing less than the remaking of Rome. Bernini was to be the Pope's adviser, confidant and trusted companion. In 1629, at the age of 31, he became official architect of St Peter's.
Baldinucci gives a vivid pen portrait of what Bernini was like at this moment of professional coronation, to which we can add his own beautiful, moodily glamorised self-portraits. He had the thick dark hair and swarthy complexion of his Neapolitan mother, Angelica, although he found the sun intolerable and would do everything he could to avoid it. We know Bernini could be witty and easy-going, but the image he wanted to project - and that was true enough - was of someone who was consumed by the sacred demands of his vocation. When Pope Urban urged him to marry so he could bequeath some of his gifts to another generation, he replied that his sculptures were his children. Once embarked on a work, Bernini gave everything he had to it: going without food, drink or rest, and becoming absorbed in the creative effort.
By the 1630s Bernini was a little drunk on his own success. As Pope Urban's favourite, he could do no wrong, and was designing the facade of the spectacular Palazzo Barberini. The tombs of the great and the good - including the one the Pope planned for himself - were his to command, as were spectacular fountains. So he took what he needed from his assistants: technical expertise, manual labour, specialised craft and, in one case, a wife.
Matteo Bonarelli had come to Rome from Lucca around 1636 and joined Bernini's workshop, where he had the usual details - angels and such-like - farmed out to him by the Cavaliere. His wife, Costanza, was, however, evidently no angel, nor especially constant. The affair between her and Bernini was apparently not his first, since Baldinucci writes of the romantic adventures, very much in the plural, of his youth. The "youth", however, was by now nearly 40, and his liaison with Costanza was obviously more than just a fling. He was, as his son Domenico candidly wrote, "fieramente inamorato" with her.
It's not necessary to have their love letters to demonstrate the intense heat of that passion, since we have something far more eloquent: a portrait bust of Costanza, created at the height of their affair in 1637. There's something about lovers' passion that makes them want to show off. Bernini has carved Costanza so lovingly that it's as though he yearned, however recklessly, to revel in the display. So Costanza's hair, drawn up in a plait at the nape of her neck, is lustrously thick; but from its loose gather falls a single lock for which the term "kiss curl" was never more appropriate. Costanza's eyes are wide, her cheeks full and peachy; and her chemise falls open, more deeply on one side than the other, in the sexiest invitation in the history of European sculpture.
What gives the bust its sensual vitality is the frankness with which Bernini has depicted his lover not as the passive recipient of his adoration, but as spitfire. Costanza breaks all the rules for the depiction of women in the 17th century. A virtue of the sex was supposed to be their quietness, but Costanza is shown in the act of speech, enormous eyes not lowered but wide open, blazing.
There came a day when someone approached Bernini and whispered (doubtless nervously, given his reputation for hot temper) that his mistress was, alas, also sleeping with someone else. That someone else was his younger brother, Luigi. That evening, at the family table, he announced that the next day he would be going to the country to see to some business. But instead he went to Costanza's house in time to see his brother emerge with her "mezza vestita" - which means, probably, not half-clothed but in her nightdress. In the violent fight that followed, Gianlorenzo, trying to kill his brother with an iron crowbar, succeeded in breaking two of his ribs. At home Bernini made another attempt to kill Luigi, this time with his sword, and when the younger brother took sanctuary in the church of Santa Maria Maggiore, Bernini was left vainly trying to kick in the door.
He had not yet exhausted his rage. That same afternoon a servant was sent to the Bonarelli house. He found Costanza in bed and there, fulfilling the orders he had been given by Bernini, he cut her face to ribbons with a razor. The servant was arrested, tried and sent to prison for his assault. Costanza was sent to prison on charges of adultery and fornication. Luigi was exiled to Bologna for his own safety. Bernini was penalised - by a 3,000 scudi fine. But his patron and friend Urban VIII then waived the fine on the understanding that now the Cavaliere would marry. This turned out to be something short of severe corrective punishment, since the intended bride, Caterina Tezio, was reputedly the most beautiful woman in Rome. Bernini did indeed go through with the marriage, never (as far as one knows) strayed again and had 11 children by Caterina.
The bloody end to Bernini's affair with Costanza occurred in May 1639, and it was around the same time that his career, hitherto a Roman rocket, stalled in flight. The two years with Costanza had also been the time when Bernini had been engaged on a project for St Peter's that matched the baldacchino for lofty ambition. Back in 1612, Pope Paul V had decided that a belltower should be built at each end of the facade of the basilica. Bernini's predecessor, Carlo Maderno, had designed those towers as relatively modest edifices, rising a single storey above the roof level of the cathedral. But, as usual, Bernini's imagination, when he took over the project in the late 1630s, inspired him to think higher and grander. With an eye - as always - to Michelangelo, he declared that his belltowers would be three storeys high, over 200ft above their pedestals, soaring to frame the dome. They would also be six times heavier than Maderno's intended towers. But they would have to be built on unstable, swampy subsoil, and Bernini was under pressure to erect them in a hurry - by June 29 1641, the feast day of St Peter and St Paul.
Two months after the unveiling, a visitor reported, "They say that the Cavaliere Bernini, who has undertaken to build a campanile at St Peter's, has failed and that the great weight of the tower will bring the facade down. This having come to the notice of the Pope, he called Bernini to him and severely reprimanded him for not having wanted to take the advice of anybody."
The Pope's withdrawal of favour was crushingly demoralising for Bernini. One source has him taking to his bed, fasting almost to the point of death. In 1644, Urban VIII died and his successor, Innocent X, ascended the throne accompanied by a reputation for austerity. Both the men and the projects favoured by Urban came under frosty scrutiny. And nothing seemed more excessive than Bernini's surviving belltower.
By the end of 1645 there were three cracks in the facade of St Peter's. There seemed no danger of the tower, much less the entire facade, collapsing, but Bernini's reputation and authority were destroyed. On February 26 1646, the Pope's decision was announced. The remaining belltower was to be dismantled, the stone to be saved for the construction of an alternative and sounder design.
An English visitor, Nicholas Stone, wrote that Bernini once again collapsed into despair, "sicke to deathe and [at once] dead as it was reported". The truth was that he was down but very definitely not out. His estrangement from the new Pope was an opportunity for lesser eminences to secure Bernini's services. And Cardinal Federico Cornaro, from an old aristocratic dynasty, grabbed it. The Cornaros were patrons of the austere order of Barefoot Carmelite Sisters, and the plan was to build a family chapel devoted to their famous reformer St Theresa of Avila. Bernini wanted - and seized - a chance for vindication. It helped, of course, that Cornaro was willing to lay out the huge sum of 12,000 scudi for his chapel.
So Bernini could, if he wished, pull out all the stops: he could create not just a sculpture but a spectacular architectural setting (to stop the mouths of critics who said he was no builder), and perhaps include some painting as well. It could be a theatrical ensemble of all the arts and, if done well, the greatest drama he had ever created. And its star player was - for Bernini - irresistible.
Theresa of Avila had died in her native Spain more than a half century earlier, in 1582, but she had been canonised only in 1622. For even after her death - as during her life - there was always something slightly worrying about Theresa: her emotional extremism, the contortions of her body graphically described in her autobiography, those raptures in which she had levitated up the walls of her cell with nuns hanging on to her habit. Perhaps they were, after all, the delusions of an unseemly hysteric?
Theresa had been a vivacious, headstrong, material girl, interested in clothes, jewels and perfume. Her father, anxious about all this worldliness, confronted her with the choice between marriage and convent. She chose the latter, although not out of an immediate surge of piety: she had heard there was more, not less, freedom in a convent than locked away as the wife of a Spanish hidalgo. As a novice, she would still be able to receive visitors - even male visitors. Life behind the convent walls, however, turned out to be less sociable than she might have expected. The habits were coarse and black, the food grim, the prayers relentless. So Theresa did what angry teenagers do: she became bulimic, stabbing her gullet with an olive twig, vomiting, wasting away.
It was not until she was in her 40s, and the exuberant girl had turned into the middle-aged sister, that something overwhelming happened to Theresa. She had spent the day praying and had begun to sing the hymn Veni Creator Spiritus - Come To Me Divine Spirit - when, of course, He did. "A rapture came over me, so suddenly that it almost lifted me out of myself. There was no doubt about it because it was very obvious. That was the first time that the Lord gave me the favour of a rapture. I heard these words, 'Now I want you to speak not with men but with angels'."
It was this experience of bodily "lift" that must have leapt from the page into Bernini's imagination. So many of Bernini's body-dramas had featured this tortured ascent - his teenage Lawrence, arching from the grid-iron; Daphne's trunk rising into the sky. His entire conceptual philosophy of sculpture was a breaking-free from weighty immobility. Now it was time for him to give form to Theresa's levitation, unlike Daphne, not in resistance to penetration, but in craving for it, as she wrote of her raptures:
"Very close to me... an angel appeared in human form... he was not tall... but very beautiful and his face was so aflame that he appeared like one of those superior angels who look as though they are completely on fire... In his hands I saw a large golden spear and at its iron tip there seemed to be a point of fire. I felt as if he plunged this into my heart several times so that it penetrated all the way to my entrails. When he drew it out he seemed to draw them out with it and left me totally inflamed with a great love for God. The pain was so severe that it made me moan several times. The sweetness of this intense pain is so extreme that there is no wanting it to end and the soul is satisfied with nothing less than God. The pain is not physical but spiritual even though the body has a share in it - in fact a large share in it."
Everything Bernini had done thus far must have seemed a rehearsal for this supremely delicate and difficult task. To raise up Theresa, Bernini drew on another of the skills he had, over the decades, brought to perfection: the variation of surface texture. The cloud bearing the saint would be roughly worked, not just for the illusion of mysterious vapour, but so that the brilliantly polished body and robe would shine the more radiantly. To keep her airborne would mean hollowing out the rock-cloud and fastening it to the chapel wall with hidden braces and bars.
There was a risk that everything might snap, that there might be another crack disaster. But it was a paltry risk beside the one that Bernini decided to take with the rendering of Theresa's face and body. What did rapture, after all, look like? What if he carved this woman, who herself had dared to describe her experience so graphically, as if at the height of her sexual pleasure, utterly abandoned to a flood of sensation, straining towards her spiritual consummation, body and soul indivisible? Who would dare challenge him? He would take his own, ample carnal knowledge and turn it into a sacred shock.
Bernini's Theresa, it hardly needs saying, is no middle-aged nun rising up the wall in her habit like an untethered balloon, nuns clinging to the hem. This woman is unforgettably beautiful, a match for the beaming seraph. They are, in their way, a couple. We see his exposed breast, infer hers. How could Bernini make visible the tide of ardent feeling washing through Theresa? Here he has the crucial conceptual insight of the entire drama. He turns her body inside-out so the habit - the protecting garment of her chastity, the symbol of her discipline - becomes a representation of what is taking place deep within her. It is, in fact, the climactic shudder itself, a storm surge of sensation cresting and falling as if the marble had been molten.
Everything that Bernini has in his repertoire is summoned to create what Baldinucci calls a "bel composto" - a beautiful, perfectly integrated fusion of all the arts: colour, motion, light, even a sense of the heavenly choir pouring music down on the scene. And the talent for which he has been most criticised, the one that has brought about his disgrace - architecture - becomes, in the Cornaro Chapel, a vindication thrown back in the teeth of his critics.
The Cornaros loved their 12,000 scudi chapel: cheap at the price. Word circulated that in Santa Maria della Vittoria, the Cavaliere was back on form. Bernini went from strength to strength: he served not just a succession of popes, but also foreign monarchs, such as Queen Christina of Sweden and King Louis XIV of France, who were elated to have the greatest sculptor in the world produce their likenesses.
It was said that, every so often over his long career, Bernini could be found at the Cornaro Chapel, kneeling in prayer before what he called the "least bad thing I have ever done". Some of us stubborn heathens may have a hard time kneeling when we see Theresa caught in her spasm of rapture. But we stare and stare none the less - as we stare at no other sculpture ever made. Perhaps the force of the spell comes from the realisation that Bernini has used the power of art to achieve the most difficult thing in the world: the visualisation of bliss.
© Simon Schama, 2006
· This is an edited extract from Simon Schama's Power Of Art, published by BBC Books on September 28, at £25. To order a copy for £23, with free UK p&p, call 0870 836 0875 (theguardian.com/bookshop). His BBC2 series based on the book starts next month.