They ran across the rear of the cohort and took position at the end of Maximius’ century, also at a right angle, parallel with the men still fighting the Britons. When all was ready Maximius cast a last eye over the situation and then took the decisive step.

‘Cohort! Disengage to the right!’

Step by step the cohort shifted its ground downriver, the men facing the Britons now concentrating on keeping tight formation rather than killing their enemies. As the Fifth Century moved out of the enemy’s reach it began to wheel round and joined with the end of Cato’s men. But now the cohort had shifted along the bank far enough to open a gap on the left flank and the Britons quickly rolled round it and began to engage the men of the First Century. As more and more of them poured out from the ford and flowed round the Roman formation Maximius glanced towards the right, anxious to complete the transformation of his cohort from line to rectangle. At last the Fourth Century cleared the ford and at once wheeled round to form the last face of the defensive formation. Slowly, with shields facing out on all sides the cohort edged away from the ford and back down the track towards the rest of the legion, their only chance of salvation now.

More and more of the enemy had crossed the river and fell at once on the retreating Romans. Cato, in the front rank of his century, kept his shield aligned with the men on either side of him and slowly sidestepped as blows landed continuously on the curved surface. He kept glimpsing the enemy, and repeatedly thrust his sword out to keep them at bay. Now and then his blade struck a man and there would be a cry of pain, or shout of rage. As the cohort crept away from the ford it too suffered casualties. The wounded men dropped out of line, and the spaces they left were quickly filled by men from the next rank. Those injured who could still walk were shoved through to the centre of the formation, the others were left where they fell, to be butchered the moment their comrades had passed by. Once, this had seemed cold-blooded to Cato. Now he accepted it as a grim necessity of war. Much as he dreaded a disabling wound that would leave him helpless on the ground, Cato knew he could not expect others to sacrifice their lives to save his. That was the harsh code of the legions.

A sharp cry of agony sounded close to his left. Cato did not even glance round, not daring to risk tearing his intent gaze away from the enemy. Yet he was aware of someone on the ground as he sidestepped along with the rest.

‘Don’t leave me!’ a voice called out, shrill with terror. ‘For pity’s sake, don’t leave me!’