Beside him Macro smiled approvingly. The optio was finally acting like a soldier in battle. No longer coy about shouting out encouragement to men far older and more experienced than him, and cool-headed enough to know how the cohort must fight in order to survive.

The heavily armed Britons hurled themselves on the Roman shield wall with a fanatical savagery that horrified Cato. On either side of the box formation, the more lightly armed natives closed in on the flanks, screaming their battle cries and urged on by the Druids. The priests of the Dark Moon stood a little behind the fighting line, pouring curses on the invaders and calling upon the tribesmen to sweep this small knot of Romans from the British soil they defiled with their eagle standards. But religious fervour and blind courage provided no protection for their unarmoured breasts. They fell in large numbers before the lethal thrusts of swords designed to make short work of such foolish heroics.

At length the British heavy infantry became aware of the grievous losses that were piling up at the front of the armoured square, and still the Roman line remained unbroken and unwavering. The Durotriges began to shrink back from the terrible blades that stabbed out at them from between shields that all but hid their enemy from view.

‘We’ve got ‘em!’ Macro bellowed. ‘Forward! Keep forcing them back!’

The Durotriges, brave as they were, had never before encountered such a ruthless and efficient foe. It was like fighting a great iron machine, designed and built for war alone. It rolled forward without pity, impressing upon all who stood in its path that there could be only one outcome for those who dared to defy it.

A cry of anguish and fear grew in the throats of the Durotriges and flowed through their milling ranks as they realised the Romans were prevailing. Men were no longer willing to throw themselves uselessly at this moving square of impenetrable shields that was cleaving its way through ranks of swords and spears. As the Durotriges at the front recoiled, the men in the rear began to step back, at first just to keep their balance, and then their feet picked up speed, as if of their own will — carrying them away from the enemy. More men followed and scores, then hundreds of Britons peeled away from the dense mass of their comrades and fled down the track.

‘Don’t fucking stop!’ Hortensius roared from the front rank of the First Century. ‘Keep advancing. If we stop we’re dead! Forward!’