Well, you know the rest. Ten years of on-and-off glory, then Mark Anthony's falling-out with Octavian (later the Emperor Augustus), their defeat at his hands, the suicides, the final takeover by Rome, the end of the Ptolemaic dynasty as Cleopatra's children died in obscurity, the birth of the legend, the stuff of a million paintings and poems and operas and plays and films. All this, the British Museum exhibition recounts dispassionately. You see the latest finds, as dredged from the harbour at Alexandria, including a strangely haunting bust of (it is thought) her son Caesarion. I'd like to know more about Sun and Moon, but the problem here is an eternal one: Cleopatra and Mark Anthony lost. Octavian/Augustus won. It's the winners who write the history books and destroy the traces of the vanquished. We know plenty about the Augustan era, but what survives of the decade's rule in the Eastern Mediterranean by the famous lovers is scanty indeed.

Which is why Cleopatra is anything we want her to be, all the more potent a symbol for being elusive as an image. Yet while it is all about her, the central figure is virtually absent. The other key players are all there: crafty Caesar, no oil painting he: Mark Anthony himself, a nobler figure but still scarcely a matinee idol: Octavian/Augustus, who as victor of course is depicted as ruggedly handsome: Alexander the Great, ditto; Pompey, who modelled himself on Alexander; even a rather touching head of Mark Anthony's neglected politically-expedient wife, Octavia.

The Ptolemies, however, are present as a dynasty rather than as individuals. Argument continues to rage over exactly which one is which. Are you looking at Cleopatra, or her rival sister, Arsinoe, or even her mother or grandmother? Details of the head-dress they wear, details of the positioning of the arms and what they hold, can indicate one rather than another, but this is no exact science. And even given the conventions of statuary of the day, this unhealthily closely-knit family obviously all looked pretty much like each other anyway.

Did Cleopatra VII bring something different to the Ptolemaic gene pool in appearance and attitude, or did she merely live in interesting times that happened to be recorded diligently by the Romans? No-one has a clue. Which is why - although the meaning of the images is not sufficiently explored - the most immediately evocative images to be found in this exhibition are not the precious ancient objects, but the diorama backdrop of Cleo as depicted by painters, society women at fancy-dress balls, actresses - and one actor/director, Mark Rylance, who played the role in 1999 at Shakespeare's Globe in an authentic all-male cast.

This last is an interesting, if unintentional, gloss on the Ptolemaic habit of having a joint male-female monarch comprising a brother and sister - looking very like each other - married to each other. By breaking free of this tradition and making sexual and political alliances with Rome, Cleopatra extended the rule of her dynasty for a few years only. But in the process she established herself for ever in the popular imagination as all woman. That was her smartest move.