During the autumn of AD130, a flotilla carrying the Roman emperor Hadrian and his entourage was making stately progress along the Nile. In the course of a grand tour that had so far encompassed Greece, Turkey, Syria, Arabia and the province then known as Judaea, the imperial retinue had reached just over halfway between Cairo and Aswan. The emperor himself had every reason to feel satisfied. Rome’s eastern territories showed all the signs of beneficent rule; while far away to the north, the limits of civilisation were now marked by a stark wall - a monument that would bear his name down the ages.

What happened in Egypt was perhaps little more than a banal boating accident. But for Hadrian it was a personal tragedy that registered throughout the Classical world - and still has resonance today. Among the imperial courtiers there was a young man called Antinous. Originating from the Asian province of Bithynia, Antinous had entered service as a pageboy when he was only 12 years old. To say that he was “like a son” to Hadrian is to put a charitable slant on their rapport. It was customary for a Roman emperor to assume the airs, if not the divine status, of the Olympian god Jupiter. Antinous, it seems, played Ganymede to Hadrian’s Jupiter: said to be the emperor’s “favourite boy”, very likely his “cup-bearer” or catamite - and apparently cherished as such in full public view.

Antinous lost his life in the river. That is really as much as anyone knows. No eye-witness accounts are available, and the few surviving testimonies regarding the incident are brief and prejudiced. Soon after Hadrian’s own death, in AD138, rumours circulated that Antinous had not drowned accidentally in the Nile. One story told of the emperor’s curiosity about Egyptian mystery cults, his fascination with the magical phoenix-bird of Heliopolis, and the possibility that Antinous volunteered to die as a means of gaining immortality for his master. Another hostile theory insinuates that Hadrian used Antinous for some kind of human sacrifice, perhaps in grotesque mythical mimicry of the Egyptian god Osiris. The more prosaic explanation is that Antinous simply slipped overboard - and was gobbled by crocodiles before anyone could save him.

Whatever the cause of death, its effect upon Hadrian was dramatic. “He wept like a woman,” it is reported scornfully in the annals of ancient Rome. But Hadrian did more than weep. He promptly ordered that a city be founded by the place where his precious boy was lost, to be called “the city of Antinous” (Antinopolis), a site that survives today. And if that were not enough, Hadrian pronounced that a new god be recognised throughout the empire. Antinous, henceforth, would be consecrated as a cult figure.

So it was that Hadrian shared his boyfriend, posthumously, with the world at large. The effect of “canonising” Antinous was to export the boy’s image as a numinous presence to all Roman citizens. Full lips, slightly pouting; a fetching cascade of curls around his soft yet squared-off face; somewhat pigeon-breasted, but winningly athletic, his backside making an S-curve that begs to be stroked... one could rhapsodise further, but it is more telling to stress the sheer quantity of production. From colossal heads and full-scale statues to miniature likenesses on coins and oil-lamps, the features of Antinous were replicated far and wide, in places as diverse as Libya and Georgia on the Black Sea. And now the Henry Moore Institute in Leeds has become temporary shrine to a selection of Antinous images from various collections around Europe. Curated by Caroline Vout, whose doctoral dissertation was devoted to this subject, it is an exhibition that celebrates the apotheosis of an ancient celebrity: Antinous, who remains famous because he was famous - and good-looking.

What went on inside the mind of Antinous we shall never know. We have only his image, and that is a posthumous mask. He was commemorated as one doomed to a premature end. The first impression from the material gathered in a new exhibition at the Henry Moore Institute in Leeds is of a moody and melancholic individual, every bit as vacuous as those unsmiling types routinely seen in advertisements for Italian designer underpants.

The image of Antinous was itself used not long ago in a campaign for Fendi perfume. But how is it that the enchantment of Antinous has survived over two millennia?

To the romantic historian - notably Marguerite Yourcenar, whose Memoirs of Hadrian (1951) was an exercise in reading Hadrian’s mind - the power of Antinous stems from a tale of tragic romance: the pederastic relationship that had to be cut as Antinous grew into manhood; a married emperor who ultimately preferred his own sex. A more cynical analysis, however, argues that the numerous images of Antinous were generated for the sake of a religious revival. Hadrian knew about the Christians, whom he regarded as harmless idiots; he waged war against the Jews, who challenged his authority. His priority was to affirm the rites and values of the Classical pantheon. So he presented Antinous as the new Dionysos, a second Apollo, the great god Pan reborn. Statues of Antinous duly appeared in these and other divine disguises, heavily dependent upon the Classical Greek religious logic that the gods were similar in form to outstandingly beautiful mortals.

There must be some truth in this explanation, because the invective subsequently directed at poor Antinous by the Church fathers was singularly hostile. Origen and others railed against him as the plaything of a sodomite, and urged the destruction of his statues and shrines. But Christian condemnation did not eradicate Antinous. His images may have been knocked down and buried - but many were made of solid marble, and they would surface again. In the 16th century, one was excavated, and was proudly put on display in the Vatican. Typically, it was Raphael who adopted Antinous as an artist’s model; soon enough Antinous was redeemed, and transformed from a debauched pagan sinner into a clean-living, ideal male nude. For the German art-historian J.J. Winckelmann, two centuries later, the twin identities of Antinous as embodiment of Classical poise and object of homoerotic desire were hardly separable. By the time Oscar Wilde composed his moralising tale The Picture of Dorian Gray (1891), it could be said that the face of Antinous had illuminated an entire epoch of art.

So Antinous survives as an icon within the western visual tradition. But there may be more to it than that. The Antinous phenomenon seems to confirm what scientists have proposed: that beauty in both men and women is an absolute, a quality that prevails down the ages. The facial matrix and the physique of Antinous correspond to certain well-established expectations of what constitutes human beauty: a symmetry of features, and a calibrated sequence of proportions, that combine to satisfy our collective recognition of what is handsome in a man or pretty in a woman. It has even been claimed as a cross-cultural phenomenon. According to research, the inhabitants of a village in rural China, totally secluded from the western world, will (if asked) judge that David Beckham (for example) is a good-looking man. Computer analysis then shows that it is a millimetric arrangement of parts that gives us the whole we conventionally salute as beautiful.

Unlike Hadrian, who aspired to be a philosopher-king, we may not proceed to equate beauty with goodness, still less consider it a route to deification. But to gaze upon the image of Antinous is irresistibly to acknowledge that Hadrian was a judge of exquisite, and universal, good taste.