The Emperor who holds up a mirror to our times

Should anyone doubt that we are living in a golden age for museums and exhibitions, the British Museum's magnificent new show on the Roman emperor Hadrian should put them right. Painstakingly constructed and utterly compelling, this latest blockbuster is testament to the sheer ambition of London's premier museum under the inspired leadership of Neil MacGregor.

But its achievement goes beyond even that - for not only does it shed new light on one of history's greatest empires, it offers plenty of lessons for Hadrian's modern-day successors.

Our fascination with the Romans has deep roots: the Victorians saw them as forerunners of Britain's global empire, while even now audiences thrill to sword-and-sandals epics such as Gladiator and the BBC's controversial Rome. And all the grandeur, romance and might of the empire at its zenith are there in the British Museum's new show, from the colossal busts of the ruler and his family - some never before seen - to the Vindolanda tablets, found near Hadrian's Wall, with their intelligence reports on the empire's tribal enemies.

But the real star of the exhibition is Hadrian himself - one of history's great enigmas, and a brilliant politician whom our present leaders would do well to study. For the bearded emperor makes even Tony Blair look transparent and uncomplicated. A Spanish parvenu who loved all things Greek, a ruthless politician who adored philosophy and wrote poetry, a military man who put his armies into reverse gear, he bewildered his subjects and historians alike.

The parallels with the present day are extraordinary. When Hadrian assumed power in August AD117, the Roman army was badly overstretched, facing rebellions everywhere from Britain to the Middle East. And the first thing that Hadrian did - showing the cool, decisive leadership that was to become his trademark - was to pull Roman troops out of their recently conquered territories in what is now Iraq, where local insurgents were running riot.

Giving up on Iraq was immensely controversial-for the Romans prided themselves-on their record of military victories-Unlike our own troops, the Roman army was well funded and hugely respected, a symbol of civilisation and a route to political success. At home, citizens even bought their groceries with coins displaying scenes from the battlefront; the shock, therefore, was all the greater when Hadrian announced that Rome was withdrawing.

What Hadrian recognised - and what his successors would do well to learn - is that even the greatest empire has its limits. Rome continues to fascinate because its sheer scale and ingenuity leave us in awe. As the exhibition reminds us, it covered not only the modern European Union but also North Africa and the Middle East, uniting hugely different ethnic and religious groups in a vast zone of Roman law and free trade.

And yet while the dazzling array of statues and artefacts brings home the stunning sweep of Roman power, Hadrian's most famous achievement - the great wall on the Scottish border - makes the point that every world power must stop somewhere.

If that makes Hadrian sound like an emperor for our times, there is more. Often seen as a kind of Roman Lib-Dem - all beard, sandals and multicultural enthusiasms - he emerges here as a master of political spin.

Despite his Spanish background and provincial accent, he made every effort to portray himself as a traditional Roman, striking conventional poses in statues sent all over the empire, one of them preserved here in superb condition. And unusually for an emperor, he wore a beard - another canny bit of presentation, associated both with the army and with Hellenic philosophy, and thereby appealing both to military conservatives and to the Greek speakers of the empire's booming East.

Hadrian's military associations were no affectation, however. Like John McCain, he prided himself on his war record; the British Museum even displays the text of a speech in which the emperor advised his troops on their tactical manoeuvres.

And the exhibition also reminds us that Rome was an empire based not just on law and trade but also on bloodshed - - for among Hadrian's legacies was his brutal suppression of a huge Jewish revolt, leading to the banning of Judaism and the deaths of perhaps half a million people. One bust from Jerusalem shows him glaring ahead in full bronze armour, the very image of a ruthless imperial despot.

Modern politicians often struggle to come across as recognisable human beings - and we can all think of one high-profile example - yet Hadrian comes over as a painfully human, fleshand-blood figure. Busts show him with creased earlobes, which medical experts now regard as an early sign of the heart disease that probably killed him. And the most fascinating part of the exhibition is the section on his personal life.

The catalogue bluntly describes him as gay but adds that the Romans did not have our sense of sexual classification. They were certainly a lot more tolerant than we are. For as numerous exhibits make clear, the middle-aged emperor did fall madly in love with a Greek boy called Antinous, just 13 or so, who became his constant companion. When Antinous drowned in the Nile, the griefcrazed Hadrian commissioned medals, statues and even cities in his honour, and the cult of Antinous - who was declared a god - became the fashionable religion of the day.

In Hadrian's anguish at the death of Antinous, we get a sense of the real man behind the stern, bearded busts. And the British Museum has one last tantalising glimpse for us - a fragment of Hadrian's autobiography, now lost.

Even though we can never read his memoirs, he remains the Roman world's single most intriguing figure, ancient and modern all at once, a decisive leader whose life encompassed the strategic realities and cultural ambiguities of his day.

While this splendid exhibition, gathering rare artefacts from 31 different museums across the world, should be the blockbuster of the summer, we can only hope that our modern leaders will visit it and take note. For this exhibition is not merely a splendid celebration of ancient grandeur; it holds up a mirror to our own times.

Hadrian opens at the British Museum on Thursday 24 July.