The cohort had another problem as it stood to in a hollow box astride the track. In the centre, ringed by half a century of nervous legionaries, squatted the prisoners taken at the settlement. They were excited, and craned their necks for sight of their comrades, whispering urgently to one another until a harsh shout and a brutal blow of a shield stilled their tongues. But it was like damming an irresistible current and as soon as one section was silenced, the whispering flowed elsewhere.

‘Optio!’ Hortensius shouted to the officer in charge of the prisoners. ‘Get ‘em to shut their fucking mouths! Kill the next Briton who opens his trap.’

‘Yes, sir!’ The optio turned back to the prisoners and drew his sword, daring them to utter a sound. His posture was eloquent enough and the natives shrank back in sullen silence.

‘What now, I wonder,’ said Macro.

‘Why don’t they attack us, sir?’

‘No idea, Cato. No idea.’

As the light in the sky thinned and the gloom of late afternoon thickened, the two forces stood in silent confrontation. Each waited for the other to surrender to the imperative need to do something to end me tension wearing away at their nerves. Macro, veteran though he was, found that he was rapping his fingers on the rim of his shield and was only made aware of it by the curious sidelong glance of his optio. He withdrew his hand, cracked his fingers loudly enough to make Cato wince, and rested his palm on the handle of his sword.

‘Well, I’ve never seen the like before,’ he began conversationally. ‘The Durotriges must either have the best self-control I’ve ever seen in a Celtic tribe or they’re even more nervous of us than we are of them.’

‘Which do you think it is, sir?’

‘I don’t think I’d bet much on them being scared.’

As he spoke, the enemy line parted to let a handful of men through. With a thrill of terror Cato saw that their leader wore an antlered headpiece and that he and his mounted followers were swathed in the same black robes they had worn before the ramparts of the Second Legion when their leader had beheaded the navy prefect, Maxentius. With a slow, deliberate and menacing gait, the Druids walked their horses up towards the cohort and gently reined in, just out of javelin range. For a moment the only movement came from their horses gently pawing the ground. Then their leader raised a hand.

‘Romans! I would speak with your leader!’ The accent was marked, betraying the Druid’s Gallic origins. His deep voice echoed flatly off the snow-covered slopes of the vale. ‘Send him forward!’