The army was changing too. Posted for ever at static frontiers, the troops understandably became more loyal to their local commanders than to any distant emperor - and generals who had once looked beyond the borders of the empire for glory were now forced to look inward to pursue their ambitions. These centrifugal tendencies spun off one usurper after another, even in Britain. It had taken a new breed of tough, ruthlessly competent soldier-emperors to pull the empire out of a crisis that might have been terminal. But it seemed to Thalius that the character of the empire had been transformed in these trials - and now, under a new emperor, it might be transformed again, even more drastically.

And Thalius, amateur historian, had looked further back in time still. Many of his acquaintances imagined that Constantius’s Invasion of Britain two decades ago had been the first Roman assault on the island - as if Britain had always been Roman. But there had been a history, of a sort, even before Claudius’s adventure three centuries ago. Thalius had read, fascinated, of British rebels who had sought to throw off the yoke of Rome, calling themselves Brigantian or Iceni or Catuvellaunian - names Thalius had thought only referred to Roman administrative units. He had no idea what the deeper history of these lost nations might have been. He had been astonished to find in his family research that he himself was, at least partly, of Brigantian blood.

Now the British saw themselves as Romans - and if they rebelled, like Carausias, they did so within the system rather than trying to overthrow it. The people of old, his own ancestors, had had minds of a different quality from the modern, Thalius thought. He wondered how much else had been changed, or lost, in the Roman centuries.

There was a noise outside. Volisios’s office had small blue-tinted glazed windows; looking out, Thalius saw a band of workers being brought up from a mine shaft and marched off to some rough barracks. As they passed they glared at the overseer’s hut. Thalius shivered, despite the heavy irons that bound the slaves’ legs and necks.

Volisios stood beside him. ‘You don’t need to be afraid of them,’ he said with faint contempt. ‘Most of them have been whipped so hard all their lives that even if you took their chains away they wouldn’t raise a hand against you. You have to do it, you know.’

‘What?’

‘Treat them harshly. I know what you’re thinking, that this is a brutal place. But I have to crush my slaves to get every last drop of blood out of them, because the tax men squeeze me for profits. It’s the way things are.’

‘But is this the only way?’ Thalius murmured, suddenly appalled by Volisios’s bloodless rationalising.