"Leonardo da Vinci pointed us towards paradise," said Picasso.

commissions in Rome that changed art history - his own tomb, and the Sistine ceiling. Michelangelo never finished the Tomb of Julius II , but the image of Moses he carved for it is, in a deferred and complex way, a portrait both of Julius and himself: two men who were terrible, terrifying, like Michelangelo's Moses . But Julius got another of the world's great portraits, and this time a more conventionally pleasing one. Raphael was in his late 20s when he painted his Pope Julius II . Raphael is a difficult artist, nowadays, to get a handle on. So much of what made him, for previous centuries, the ultimate artist is no longer very meaningful to us: the classical tradition, which Raphael introduced into painting more gracefully and purely than anyone, is no longer at the heart of culture. We can't worship Raphael in the way that Ingres did, as the master of classical balance and harmony.

 What you have to remember, in comparing Raphael to his peers Leonardo da Vinci, Michelangelo and Titian (all of them in their turbulence more meaningful to us than the gracious young courtier from Urbino), is that he died when he was 37. His late paintings such as Saint Michael (1518, the Louvre) and Saint Margaret (the Louvre version, also 1518) possess an emotional power and depth that suggests he would have broken out of the elegant discipline of his facility, and created paintings as profound as Leonardo's Last Supper or Titian's Pietà . If he'd lived 20 more years, we'd rate him the greatest of all. As it is, he is sublime. "Leonardo da Vinci pointed us towards paradise," said Picasso after comparing their paintings in the Louvre, "but Raphael gives it to us." I was stunned when I looked at Julius II floating in front of me, with his waterfall of white crinkly fabric, his deep red velvety robes, the huge gold acorn symbols of the della Rovere family on his throne, the green background - and that face, turned down in melancholy, so warmly fleshy in Raphael's soft smooth brushwork, his beard (grown to mourn the rebellion that overthrew his rule in Bologna, which incidentally destroyed a bronze statue of him cast by Michelangelo) a prickly white wisp. What a face. What a painting. And as I now feel free to say: what a story. It is extraordinary, looking on this man dead almost 500 years and feeling his personality, downcast at a moment of defeat, unambiguously real and alive, here in the room with you. Raphael's painting has such deep, natural conviction it makes you believe you are meeting Pope Julius II. And even though Raphael catches him in a moment of sensitivity and sobriety, you sense the danger of this man - his emotional intensity. This is what made Julius a loose cannon, a point the Bolognese made when Michelangelo's statue was melted to make a cannon, named the Giulia after him. He was "impetuous" and if Raphael - by all accounts a great charmer -puts him at his ease, he is relaxed enough, uninhibited enough, to display everything he feels: a terrible self-pity because the city he conquered overthrew his rule. What it is to be a warrior pope. So many regrets, so much revenge to take. Of course it's flattering. Like Marlon Brando's Vito Corleone, a man of power and violence is made to seem uncannily tender and loving. Trying to think of a modern analogy, I come up with The Godfather - not a work of contemporary art. There's something wrong with art if it can't engage us like Raphael's portrait of Julius II does. This is a great painting; it is also great drama and great history. All the best portraits are. That's why the Old Masters have dominated Portrait of the Week - because when you're looking at Velázquez's Innocent X , say, you apprehend both the artist's formal and intellectual power and the terror of his subject, not to mention his dialogue with Titian's papal portraits and behind those, Raphael's Julius II , which Titian copied. What I learned from Raphael is that, yes, the portrait has to be seen as art not just pictures of people, but that the great portraits are narrative, dramatic masterpieces, that the stories they tell are part of their glory. Starting out suspicious of the portrait, this series fell in love - not just with Raphael, but with Julius II, the old monster.

Portraiture is serious art. It is modern art - Van Gogh and Picasso, Warhol and Bacon prove that. I haven't seen much contemporary art that really fitted in this series (some got in anyway). I used to share the suspicion of anecdote, triviality and populism that makes good artists run a mile from portraiture. In Britain, with its very old culture of individualism, where art was damaged in the 18th century (as William Blake complained) and since by an anti-intellectual obsession with portraiture that still makes the NPG the middle-class Madame Tussauds, it's understandable that self-respecting artists don't want to make portraits. It's a shame. J.Jones Guadian.