"The last sodomite of a dying tradition, parodying Michelangelo and stealing the light from Leonardo yet surpassing them both in emotion. In St Ursula, the final altarpiece, still drying as he died, there is a calm in the face of violent death that removes the work from the contortions of his Baroque contemporaries, the man-hating Artemisia Gentileschi's Judith and Holofernes, where the blood drips off the canvas on to the gallery floor, the sugary ecstasies of Bernini."
Thus wrote Derek Jarman in his book to accompany the release of his film about Caravaggio in 1986. It is one of the few fictional, as opposed to documentary, films about an artist that actually sheds light on his work rather than obfuscates it, as in the absurd Lust for Life with Kirk Douglas as Van Gogh and Anthony Quinn as Gauguin. The Royal Academy, which so often runs dreary videos to complement its exhibitions, ought perhaps to show the Jarman feature film in one of its adjacent small rooms. And, given the huge publicity for this great exhibition in Burlington Gardens, Channel 4, which is a part owner of the film anyway, should surely screen it while the show is on: it closes on 16 April before moving on to its spiritual home in Rome.
If Caravaggio is the star, then Artemisia Gentileschi is the female lead, and Jarman, while right about him, is seriously off beam about her.
Beverly Louise Brown, the principal curator of the exhibition, which will, deservedly, become one of the RA's big blockbuster money-earners, says that it is about "the international confluence of artistic talent in Rome around 1600 that fostered what would become known as baroque art".
The catalytic moment came when, a few months after Clement VIII became Pope in 1592, Michelangelo Merisi da Caravaggio arrived in Rome. He stayed until he killed a man over a wager on a tennis match. He then went on the run, painting further masterpieces in Messina, Palermo, Naples and Malta. This resulted in, among other things, the only known cultural benefit of my national service, when I discovered, during 15 months on Malta, his vast The Decapitation of Saint John the Baptist in the cathedral in Valletta. His largest ever painting (roughly 12 feet high by 17 feet wide), it is - perhaps presciently, given his death two years after he finished it in 1608 - signed in the blood flowing from the saint's neck on to the ground. Small wonder that Caravaggio has attracted almost as many biographies as art monographs, and I know of at least one distinguished art historian who wrote a novel about him.
Spending various half-hours stolen from military chores to look at the Baptist, and his smaller companion piece devoted to St Jerome, sparked off a lifelong admiration that makes a visit to the RA, with no fewer than 15 of Caravaggio's works (10 per cent of the 143 paintings on view), a kid-in- a-candy-store time, not least because six of the exhibits are not travelling on to Rome.
Given that the show is, reasonably enough, restricted to what was painted in Rome, one cannot legitimately mourn the absence of any pictures Caravaggio created on his post-Roman travels. It may seem churlish, amid the selection of so much glory, to cavil at a single omission, but I do think a great opportunity has been missed - and it won't come again in most of our lifetimes - in not showing both versions of The Lute Player. The RA has the New York Metropolitan Museum version, done for Caravaggio's most influential patron, Cardinal Francesco Maria del Monte. If only it had taken the opportunity also to show the earlier version, painted two years before for Del Monte's competitor as artistic patron, the Marchese Vincenzo Giustiniani. They have so much in common and yet are so different that it is a shame one cannot gaze at both simultaneously, not least because the Hermitage, which owns the Giustiniani version, is so clearly (see Somerset House) in a new and most welcome lending mood.
Still, the joy of seeing the Metropolitan's picture together with The Musicians is enough for most of us. This painting, sadly, has been much damaged over the years; the figure on the left with the grapes used to sport the wings and quiver of Cupid, and the canvas has been cut down on the left. But even in its less than pristine state, it is a dazzling work, second only in that genre to The Lute Player.
The androgynous nature of the lutenist, and indeed of some of the musicians, is typical of Caravaggio, and this is presumably provided, at least in part, for the delectation of his patrons. The lutenist is essentially a boy, but given that Roman boys of the time did not look like Mick Jagger or have access to plastic surgeons with collagen, those huge, voluptuous lips lead you straight to the feminine aspect, as does the decolletage of the torso, whose white fabric appears to conceal breasts. Still, one must not see Caravaggio in post-Freudian terms only. As the magisterial Grove puts it: ". . . his demonisation by 17th-century critics was by turns crude and subtle, and modern assessments can be equally one track, either in the inclination to brand him a psychopath or in the tendency to give centre stage to his homosexuality".
There is a great deal of sexual ambiguity in many of his pictures, and some of his male models are sumptuously pretty, but his sexual tastes and his brawling no more detract from his genius than does that of Christopher Marlowe from his drama.
What is so astounding is Caravaggio's dominance of a Rome that housed at or around the same time Rubens, Guercino, Guido Reni, Simon Vouet, Theodor Rombouts, Gerrit van Honthorst, Domenichino, Adam Elsheimer, three Carraccis, two Gentileschis, Paul Bril, even Jan Brueghel the Elder. His daring flights of chiaroscuro and his relentless divination of human frailty were unrivalled, and left a trail of influence that is hammered home in every room of the display at Burlington Gardens. Indeed, so pervasive was his influence that one can, perfectly justifiably, "spot" another Caravaggio on the other side of one of those vast rooms and, on closer inspection, find that it is, in fact, a (wholly admirable) painting by Salini or Manfredi.
The RA show, quite rightly, is not concerned with the reverberations beyond Rome. When one looks at Caravaggio's Cardsharp and Gypsy Fortune Teller, of course one cannot avoid comparing them with the lesser pictures of Simon Vouet on display here. That's what good curating is about. But one also cannot stop one's mind wandering to the most Caraveggesque of French painters, Georges de La Tour. La Tour probably spent some time in Rome, but only after Caravaggio had left in a hurry, and probably only after his death. But there were well-trodden paths from Rome to France, as well as the other way round, and it is impossible to contemplate La Tour's low-life masterpieces, The Fortune Teller at the Metropolitan or The Cheat with the Ace of Clubs at Fort Worth, or his various candlelit penitent Magdalens, without seeing the wholly beneficent ghost of Michelangelo Merisi.
One of the many glories of the exhibition is the opportunity to see several versions of the same subject by Caravaggio and his contemporaries. One of the most instructive, particularly for those with a taste for Grand Guignol, is the three paintings of Judith and Holofernes by Caravaggio (1599), Adam Elsheimer (1601-03, once owned by Rubens and now in the V&A) and Artemisia Gentileschi (1611-12).
X-rays of the Caravaggio canvas show that he originally painted Judith, a stunningly beautiful Roman girl without a scintilla of androgyny, bare breasted. What we see now is a seductive woman, fully clothed, her face slightly frowning but otherwise calm - even aloof - decapitating Holofernes with chilling ferocity; while her breasts are covered, her nipples are erect. It is a terrifying picture, not least because Judith's servant, Abra, to keep the erotic content highly charged, is depicted as a cruel, wizened old procuress.
The Elsheimer, a small oil on silvered copper, measuring only 24 centimetres by 19, is less overtly erotic, and less horrible despite the gushing blood. It certainly echoes Caravaggio's version, but is particularly interesting because it, too, probably influenced Gentileschi. Ultimately, the Gentileschi is, in its brilliant chiaroscuro and its savagery, very much inspired by Caravaggio. How could it not be?
But, ironically, it is much less erotic than the Caravaggio. Jarman certainly got it wrong in his description of this picture. It has become the, rather obvious, received wisdom that in this painting Artemisia is getting her revenge for being raped by her father Orazio's colleague Agostino Tassi, as nasty a piece of work as even turn-of-the-century Rome had to offer. The story is well told in Germaine Greer's The Obstacle Race, and I believe Greer, rather than Jarman, when she writes: "The abortive [rape] trial had left Artemisia nothing but her talent. It also removed the traditional obstacle to the development of that talent. She could no longer hope to live a life of matronly seclusion: she was notorious and she had . . . to take advantage of the fact."
Greer also believes that, in her composition of the picture, Gentileschi "decided to outdo her predecessor". I do not think she succeeded; but then, what contemporary of Caravaggio, whether male or female, possibly could? However, Artemisia's work in this case is at least an advance on Orazio (who had painted the subject himself) and, by any standards, a great painting. It may not be man-hating or an act of revenge, but it is redolent of an extreme brutality, and the rictus of Holofernes's death agony and the sightlessness of his open eyes are unforgettable.
Not all the art on display is violent or gory or low-life. There are marvellous portraits, including a superb Van Dyck and a masterly Domenichino, presaging Ingres in his Roman period, as well as flawless landscapes - particularly by Brueghel and Bril. There is also a virtuoso Venus and Mars by Carlo Saraceni, which totally eclipses its neighbour, The Judgement of Paris by Rubens.
I doubt if there will be a better or more exciting exhibition in Britain this year. It is splendidly hung, not least because the various altar paintings have a room to themselves. They are suspended above carefully modelled, altar-height wall projections, so that we can look at them as if in situ in the churches for which they were commissioned.
The catalogue is extensive, exemplary and, with more than 200 colour plates, a steal at £25. Thames & Hudson also has a hardback at £45. I am only sad that the critics' view on press day was, as is now the fashion, marred by a guided tour in which, on the whole, non-art-critic journalists move like an elephant herd from room to room. Easy enough to dodge, I suppose, but it's harder to get around self-regarding TV broadcasters, standing with their camera men for ages, four square in front of the painting you want to examine. Surely this should all be done on another day?
"The Genius of Rome 1592-1623" is at the Royal Academy, London W1 (020 7300 8000), until 16 April
Tom Rosenthal is currently completing a monograph on Sidney Nolan