Hadrian at the British Museum

We all know the wall: that long line of stone that rises and falls across rough northern landscapes. It is one of the wildest and loveliest of our tourist spots. But the Romans who once paced its bleak ramparts with their spiked wooden pila were protecting the northernmost perimeter of the world's greatest empire: the empire that - stretching from Scotland to the Sahara, from the Atlantic to the Euphrates - was ruled from AD117 to AD138 by Hadrian.

But what do we know about him? The British Museum, fresh from a success in which a posse of terracotta warriors ousted Blackpool Pleasure Beach from the top of our list of favourite cultural attractions, now turns its attention from China's first emperor to another great wall-builder. In Hadrian: Empire and Conflict, it invites us to speculate on what this most fascinating and complex emperor might really have been like.

This is a show that Gordon Brown should go to see. It follows the progress of an ambitious but prudent second-in-command who finally gets to power by being adopted by his predecessor, the Emperor Trajan, on his deathbed. But leadership, Hadrian discovers, is far from plain sailing. Trajan may have been a warrior hero, but things were very over-stretched. Although the effects had not yet reached the public, the empire had been brought almost to breaking point by a war in the Middle East...