Alof de Wignacourt, Caravaggio (c1607-08)

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Artist: Michelangelo Merisi da Caravaggio (1571-1610) arrived on the harsh, rocky Mediterranean island of Malta in 1607 as a known murderer. Yet for a while it seemed just the place for a warrior artist, and Caravaggio prospered. The island was the fortified headquarters of the knights of the order of St John, and in this community of armed priests the criminal artist was an instant success. After painting this and other extraordinary works, he became a knight of St John - for three months.

Whatever the admiration for his painterly brilliance and tough sword-bearing persona, the knights soon learned of their mistake. Caravaggio got into a quarrel, as he tended to; but this time was thrown into a deep dungeon. Somehow he got out of the cell, abseiled out of the fortress and fled to Sicily.

Subject: Alof de Wignacourt, grand master of the knights of St John, was described as the "absolute sovereign" of the military-religious community confined on this hard island.

Distinguishing features: This portrait is an incredible, sunset masterpiece. Alof de Wignacourt stands in the shadows, with the last dying light setting his armour ablaze. His menacing energy surprises you, perhaps because the picture is so soft at first on the eye, even unassertive. Then suddenly it hits you that this is one of the most inexplicably lifelike portraits you have ever seen.

The man is a gnarled, weathered, graceful thug, the skin of his face rough and reddened. This ruggedness is made lovely by bronze light, turning him gold and russet. There is something massive, even monstrous, about Alof de Wignacourt's armour; a booming violent enormity. The arms and legs are thick and his head pokes with some ungainliness out of the suit whose weight and lengthy strapping-on you can feel.

And then there is the pageboy: holding Alof de Wignacourt's helmet lovingly in both hands, he looks out of the painting, at us. He, rather than the grand master, is Caravaggio's point of human contact. Alof de Wignacourt looks, smiling, to the side, and Caravaggio shares with the boy the theatricality, the faked staginess of it all - a revelation that does not undermine the image, but makes it incontrovertible.

Alof de Wignacourt holds his baton clumsily, artificially, and plants his legs apart like an actor in a provincial drama - which is really what he is. Meanwhile, the short-haired boy looks pertly and secretively at Caravaggio.

The pageboy's look sexualises the painting, and its visual centre - the armoured body of Alof de Wignacourt. Caravaggio makes this armoured hulk as rawly powerful and as complicated as the other Michelangelo - Buonarroti - made men's torsos.

It's not hard to see why Alof de Wignacourt was awestruck by Caravaggio's abilities and wanted to keep him on Malta as some sort of court artist. The painting was displayed in the armoury, and perhaps this was a military man's recognition of the deep feeling for the art of war that Caravaggio expresses.

There is love in this painting - a love of things martial, and martial men. But, of course, it is dangerous, unruly. It contains the madness that keeps erupting and makes the artist's life impossible. When you sense all the intense feelings in this picture - desire as well as awe - you know Caravaggio will not really find a secure or stable home among the fiery knights.

Inspirations and influences: The definitive Renaissance armoured portrait is Titian's Francesco Maria della Rovere  (c1536-38) in the Uffizi, Florence.

Where is it? Musée du Louvre, Paris.