once that the task was hopeless, and within hours of taking the throne ordered Roman troops to withdraw, declaring: "It is better to abandon what cannot be kept." The frontier he drew still marks the border between Syria and Iraq. Hadrian recognised that the empire had its limits: he ordered his great wall to be built in northern England "to separate the Romans and the Barbarians", and focused his efforts on fortifying the pax Romana within the boundaries of the empire.

So was he an enlightened ruler?

Classical scholars have tended to cast him as a civilised, peace-loving aesthete: the best-known statue of him shows him sporting a sophisticated Greek mantle rather than a Roman toga, and a philhellene's beard (a style he popularised throughout the empire). But recent research shows that the body does not actually belong to Hadrian's head: the Victorians wrongly reconstructed the statue to suit their preconceptions of what Hadrian should look like. A more convincing image, say the curators of the current exhibition, is the huge statue of Hadrian as warrior, with his foot on the neck of a humbled barbarian.

Not a man of peace then?

Far from it. Like most emperors, Hadrian rose to power on the back of his reputation as a military leader; before coming to power he was active in the bloody wars against the Dacians on the Danube, and was in charge of Trajan's army in Syria. He was as ruthless and back-stabbing as any other high-flying Roman politician. His passage to the imperial throne was smoothed by the execution of four prominent rivals on trumped-up charges of "conspiracy". And his withdrawal from Mesopotamia was less about bringing peace to the Middle East than about liberating Roman military resources to quash other rebellions.

Where were the other rebellions?

In the Balkans as usual, in Mauretania (Morocco) and elsewhere. But Hadrian is most remembered for his ruthless suppression of Jewish uprisings. In AD 132, prompted among other things by a ban on circumcision (a practice Hadrian reviled), the Jews rebelled under Shimon bar Kokhba, the last king of Israel. The subsequent campaign of suppression lasted three years, cost Rome up to three legions, and involved great brutality. According to the Greek historian Cassius Dio, some 585,000 Jews were killed in battle. "As for the numbers who perished from starvation, disease or fire, that was impossible to establish." In an attempt to root out Judaism, which he blamed for the rebellions, Hadrian wiped Judaea off the map, renaming it Syria Palaestina. Most of the surviving Jews were killed, exiled or sold into slavery. In the Talmud, Hadrian's name is followed by the words: "May his bones rot".

And what was life like in Britain?

By the time Hadrian took the throne, the British had also suffered decades of violent repression, but guerilla warfare continued: when Hadrian visited in AD 122, it was not as a casual tourist but a military strategist. We tend to have a rosy view of his wall, built by his soldiers in four years, as protecting a civilised world of baths and temples against marauding Caledonians. But historians now think it was designed to cow and extract customs duties from tribes on both sides of the border, rather than to keep invading war parties out. The archaeological historian Neil Faulkner describes the Roman imperium as a system of "robbery with violence", while the contemporary Vindolanda Tablets show that Romans disdainfully called the locals Brittunculi: "wretched little Britons".