If Caratacus fell, then maybe the fight would go out of these demons, who seemed to know no fear as they threw themselves at the line of Roman shields. The legionaries in the front rank were starting to tire and the first two men to die were cut down and killed in quick succession. Their places were instantly filled by men from the second rank, and the retreat continued under the relentless attack. One by one, more legionaries fell, to join the native dead and wounded trampled down by the wave of warriors that flowed down the track.

Cato thrust his shield into the face of an older warrior, no less savage than his younger comrades, and backed out of the front line.

‘Take my place!’ he shouted into the ear of a legionary in the second rank, and the man pressed forward, shield out and sword ready to thrust into the mêlée. The centurion pushed his way through the dense pack of Romans, until he found Septimus, standing beside the century’s standard-bearer.

The optio nodded a greeting. ‘Hot work, sir.’

‘Hot as it gets.’ Cato made himself smile, desperate to give the impression of calm professional detachment that Macro managed to achieve. He looked up the track towards the cohort’s fortifications, now just beyond the final bend in their return journey.

Septimus followed the direction of his centurion’s glance. ‘Shall I send a runner back for more men, sir?’

The thought of more legionaries hurrying forward to support their retreat was a comforting, tempting prospect. But Cato realised that such a request, even if Tullius agreed to it, would only place more men in danger and weaken the cohort where its soldiers were most necessary: on the rampart, denying Caratacus and his warriors any escape from the marsh.

He shook his head. ‘No. We’re on our own.’

The optio nodded slowly. ‘Fair enough, sir. But we’re not going to be able to hold them back for much longer. If they break the line, we’re finished.’

The line was now no more than five deep and Cato knew that if they could not reach the fortifications soon, then the enemy would be able simply to brush aside the few remaining legionaries. He had to act now, and gamble his remaining javelins on one last cast of the dice.

Cato turned to his optio.’I'm going to give the order to use the last javelins in one volley. When it strikes, we fall back. If we’re lucky we can make it most of the way back to the cohort before the enemy come on again. Understood?’

‘Yes, sir. Is that wise - to use them all up?’

‘Maybe not. But we’d better use the javelins while we still can, eh?’

Septimus nodded.

‘Rear ranks!’ Cato shouted, his voice rough and grating in his dry throat. ‘Ready javelins. Aim long. Aim for that big bastard on the chariot!’