This time the enemy was more cautious. Caratacus had managed to rein his warriors in, and the head of the column approaching along the narrow track was composed of men carrying shields. Instead of the usual Celtic rush, the enemy advanced slowly, struggling to keep in the unfamiliar formation as a number of them held shields overhead. It was crudely handled but clearly based on the model they had deployed when Caratacus had forced the crossing of the Tamesis. If barbarians continued picking up more tricks of the trade from the legions, Cato reflected, Rome was going to have its hands full in a few more years.

Septimus gave his centurion a wry look.’Much more of this and we might as well sign them on as an auxiliary cohort.’

‘Give me an ally rather than an enemy every time,’ Cato muttered. He glanced beyond the approaching shield wall and saw Caratacus directing the operation from further down the track, well out of javelin and slingshot range. The enemy leader stood on his chariot, while an attendant was busy tying a rough dressing around his shoulder. When the front rank of the enemy column was no more than fifty paces from the Roman defences Caratacus cupped a hand to his mouth and shouted an order for them to halt. The warriors shuffled to a stop, adjusted their line, and began to spread out each side of the track, to the very fringes of the marsh. When the line was ready the men holding the upper tier of shields moved forward, into position, and then all fell still. Caratacus turned to a compact group of men standing beside his chariot and waved them up the track. Cato saw that they carried no swords or shields,just heavy haversacks hanging across their chests, and something that flickered like thin snakes drooping from their hands.

‘Slingers . . .’ He drew a deep breath and called a warning out to his men. ‘Prepare to receive slingshot! Shields up.’

All along the palisade the men lifted the rims of their shields and hunched down behind them as they braced for the fusillade of missiles that were far more deadly than arrows, and the supply of which would take a lot longer to exhaust than javelins. Cato, poised to duck down as soon as the enemy loosed the first volley, kept watch over his shield. The slingers ran down to the shield wall, then spread out to give themselves room to swing the leather cords that stretched out to the pouches containing the shot. A low whirring began to build up as the first slingers prepared to unleash their missiles.

‘Here it comes!’ Septimus bellowed. ‘Heads down!’