The Sixth Century, at the front of the square, had a clear view of the legion’s camp. Cato was tantalised by the sight but the snail’s pace of the cohort only served to convince him that they would never make it. The Durotriges would whittle down the exhausted legionaries long before they could reach the safety of the ramparts.

‘What the hell are they doing down there?’ Macro’s eyes blazed with bitter frustration at the sight of the peaceful stillness of the camp. ‘Fucking sentries must be blind. Just wait until I get my hands on them…’

To one side, the Durotriges’ heavy infantry, rallied after the night’s ferocious fighting, were hurrying past the square. Cato could only look on in despair, for the Britons’ plan was clear. When a hundred paces lay between themselves and the cohort, the enemy column moved obliquely across the face of the Roman square and quickly deployed into a battle line, with a small group of slingmen on each wing. And there they stood their ground, shouting their defiance at the cohort as the shield wall approached.

The legionaries had bested the Durotriges all night but they were now beyond the limits of their endurance. They had had scarcely an hour of sleep in nearly three days of hard marching. Bleary, aching eyes peered out of filthy faces matted with several days’ growth of beard. The younger Romans of Cato’s age had little facial hair, but their gauntness of expression made even them look years older. The rear and sides of the square no longer formed a steady line and began to concede ground under the relentless pressure from their less weary foes, who now at last scented victory. Soon the square was no longer a square, but a misshapen block of men struggling for their very survival. Centurion Hortensius’s voice, harsh and cracked, again rose above the din of battle.

‘They’re coming, lads! The legion’s coming for us.’

At the front of the square Cato looked over the ranks of the Britons — scarcely forty paces off now — and saw the cohorts trickling out of the camp’s southern gate, polished helmets glinting in the early morning sun. But they were miles off, and might not make it in time to save the men of the Fourth.

‘Keep moving!’ shouted Hortensius. ‘Keep moving!’

Every step forward closed the distance between the two Roman columns. Cato clenched his teeth and raised his sword towards the writhing mass of the Durotriges’ heavy infantry.

‘Watch it!’ Macro yelled. ‘Slingshot!’