The Batavians clashed the shafts of their spears against their shields three times, the pounding sound sending echoes back down the valley. Ahead of them the Britons blew their trumpets and screamed defiance. The tall auxiliaries then raised their shields over their faces and set up a low murmur.

Vindex’s horse flinched at the unearthly sound, tugging hard on the reins and turning full circle. ‘Think he wants to change sides.’

The murmuring slowly grew louder, the Batavians letting the sound reverberate against the boards of their green-painted shields. It built up like a tide washing ashore, the crests of the waves rising.

‘What is it?’ Vindex asked.

‘They call it the barritus,’ Ferox told him. ‘It’s a German thing. They say you can tell who will win the battle from its sound.’

The steadily rising chant began to drown the challenging cries of the Selgovae. Warriors faltered, puzzled by a war cry that had no words, but kept getting louder.

‘If those boys had any sense they’d charge,’ Ferox said, looking up the hill as he and Vindex went back behind the Batavian line.

The Selgovae did not charge as the Batavian shout reached a crescendo, but the warriors had sunk into sullen, browbeaten silence. When the auxiliaries stopped the silence was oppressive. To Ferox it looked as if the lines of warriors up on the slope were quivering. He saw a few men at the rear walking away over the saddle. He was just about to urge Cerialis to move when the prefect drew his sword.

‘The Ninth Cohort will advance. Forward!’

The Batavians stepped out, left leg first so that the shield remained closest to the enemy. They were silent, eerily so, with only the clink of armour and equipment as they went at regulation pace up the slope. Cerialis rode just behind the flag in the middle of the line, a pair of picked veterans walking on either side of his horse.

The Selgovae started to shout again, jeering at the enemies, but somehow it did not sound as if their hearts were in it. A few ran out in front of the mass, javelins ready in the hands. More were drifting away to the rear across the saddle and out of sight.

Ferox joined Crispinus as he followed some twenty paces behind the Batavians. The Britons kept yelling as the Romans marched forward in silence. The first javelins were thrown. One struck a Batavian’s shield and bounced off, its force already spent. The others did not even come close. A few of the Britons out ahead of the mass became bolder and scampered nearer. The next missiles were better aimed. A Batavian was hit on the shin, the broad head of the javelin gouging flesh. He stumbled and fell flat on his face, hissing with pain.

‘Leave him!’ an optio yelled from his station behind the rear rank.