‘Down!’ Ferox shouted. ‘Wait for the order!’ Men crouched behind the parapet. There were baskets of stones to throw every few paces, and heavy siege spears leaning beside them. Crews knelt beside their engines. He and Sabinus moved either side of one of the gaps in the parapet so that they could shelter while still seeing out. Arrows thudded into wood or rattled off when they did not strike squarely.

‘Wait!’ The ram in its wheeled shell was coming on steadily.

‘Wait!’ It was at the gap between the outer ditch. Behind the ones pushing it were several hundred king’s men, all with red shields decorated in a pattern of rosettes. Another unit followed and on either side there were bands of warriors, still blasting their horns and chanting.

‘Ballistae!’ Ferox shouted. ‘Archers!’ There were a dozen archers detached from a specialist cohort and a similar number of men who had some idea how to use a bow. They bobbed up, drew and loosed at the first target they saw. A few arrows struck the hides on top of the moving shed, but most were better aimed and warriors began to fall or stopped as they hunched behind shields. Scorpiones spat their darts, and the bigger ballistae in the corner towers had the sense to aim at the ram while they still could. The side of the shed shook as a stone slammed into it, but after only a slight pause – no doubt with their heads ringing – the men pushing it went forward again.

The chanting of the warbands turned into a mass of individual cries as they split up, some dashing on through the remaining obstacles and others going more gingerly. Ferox saw one man trying to leap the ditch only be struck in mid-air by the bolt from a scorpio and flung backwards. An auxiliary archer spun away as a similar dart shot by the enemy drove through his teeth and mouth with such force that the point erupted from the back of his helmet. Beside him, a comrade ducked and was sprayed with splinters and fragments of wood as a stone hit the parapet.

The ram was closer, but luck was with the Dacians and, just as the crew levelled the ballista in the right-hand corner tower to shoot, it was hit squarely by a great stone. The missile shattered the frame, releasing the tension in a whirl of flailing cables and fragments of timber and iron, scything down the men serving it and half of the rest of the soldiers on that lower level.

‘Hercules’ balls!’ Sabinus gasped.

Fortuna was as fickle as ever, because the ballista in the other tower aimed too low with its shot, so that the stone pitched a pace short of the ram, only to skim under the sides of the shed, ripping the legs off two of the men pushing from inside. Ferox could see a great pool of blood spreading from underneath.

‘Up!’ he shouted. ‘And kill the bastards!’ Men rose all along the parapet and began lobbing stones, javelins and siege spears into the mass of tribesmen flooding up to the walls. Some had ladders and they were vulnerable, for it was hard to carry one of those and use a shield. Warriors fell around them, but each time a ladder was dropped more men appeared to lift it again. The ram was lurching forward once more, and soon was safe from the remaining ballista, which with its next stone cut a lane through the king’s men following behind, sending up a spray of blood and fragments of shields and men. Bolts from scorpiones slammed in to knock down others so that the whole column seemed to shudder.