The Indian leader did not delay his attack any further. There was no reason to. The raven’s odd behaviour had already handed a small advantage to his enemies. The sooner they were crushed, the better. His first mistake was to send in the battle chariots.

Their wheels creaking loudly, they rolled towards the Roman lines at the speed of a man walking fast. Hundreds of infantry accompanied them, filling the spaces between to form a great wall of men and weapons. Musicians played drums, cymbals and bells, and the soldiers chanted as they came on. The noise was incredible. Used to smashing apart enemy formations with this initial charge, the Indians were full of confidence.

Then the chariots reached the covered water channels.

Which had turned the earth into a mud bath.

Simultaneously, all the lead chariots’ solid wheels sank deep into the morass. Cumbersome, hard to manoeuvre and immensely heavy, the battle platforms were not made to travel on anything other than flat, firm ground. The frustrated charioteers whipped on their horses. Valiantly obeying, the steeds pulled a few steps further. Now the chariots sank to the axles, and the attack stalled before it had even come near the waiting legionaries.

Pacorus’ response was instantaneous. ‘Loose!’ he roared at the soldiers manning the ballistae that covered their front.

The grizzled optio in charge had been waiting for this moment, and had already marked the Indians’ distance from his position. It was less than two hundred paces, a good killing range. He barked an order and the six powerful machines twanged as one, hurling pieces of stone bigger than a man’s head in a graceful arc over the Roman lines.

Romulus watched in awe. He had not seen ballistae used much since before Carrhae. The pitched battles fought by the Forgotten Legion were never large enough to require them. Today though, every shot counted. What mattered was causing maximum enemy casualties. Through this was their only chance of victory.

The volley was a good start.

The optio’s range marking was precise. The sixth stone merely smashed the front wheel of a chariot, immobilising it, but the rest found human targets. Men’s heads were cleanly ripped off, chests smashed in, limbs pulverised. The horrified companions of those hit were covered in a red mist of blood from spraying carotids. Their energy still unspent, the boulders went on to tear holes in the chariots’ sides or injure more soldiers before they fell to the ground, throwing up great splashes of mud and water.

The stunned Indians had barely time to react before the ballistae fired again. Yet more chariots were torn asunder, their crews killed or maimed. With his next barrage, the optio had his men load smaller stones and aim at the infantry. It was like watching heavy rain knock down a field of ripe wheat, thought Romulus. Gaping holes opened up in the Indian ranks as the projectiles landed, taking out far greater numbers than the previous volleys. It was a complete slaughter.

‘Stop them with the mud, then massacre the poor bastards,’ said Brennus, grimacing. ‘Very efficient. Very Roman.’

‘They’d do the same to us,’ retorted Romulus.

‘True,’ replied the Gaul. ‘And there’ll be plenty left.’

Keen to conserve the catapults’ rapidly dwindling store of ammunition, Pacorus signalled the optio to cease firing. Their volleys had pulverised the Indian attack. Already the enemy infantry were fleeing in blind panic towards their own lines.

The bucinae signalled that the First and Third Cohorts should advance at once. Leaving their heavy spears behind, they trotted forward, their caligae squelching through the mud. Romulus gritted his teeth. Their purpose was to kill the survivors.

The gruesome task did not take long. It was a necessary evil, reducing enemy numbers and badly affecting their watching comrades’ morale. Fearful and in disarray, the main Indian force looked on as the unfortunates left behind were dispatched by the legionaries. Soon the only living figures in the muddy area were those of Roman soldiers. Indian infantry lay scattered in piles while other bodies festooned the stationary battle platforms, hanging half-in, half-out as if still trying to escape.

The signal to withdraw rang out.

Concerned about the dozens of horses tethered by their traces and struggling in the mud before the immobilised chariots, Romulus was busy chopping through as many leather straps as he could. It was also a way to avoid killing injured, helpless enemy soldiers. He had set free a number of teams when Brennus grabbed him.

‘Come on!’ urged the Gaul. ‘You can’t help them all.’

Romulus glanced at their comrades, already halfway back to their own lines. On the other side, the enraged Indian leader had signalled his mahouts to move forward. With ponderous steps, the now calm elephants began to advance.

‘We don’t want to be caught here when those arrive,’ said Brennus.

Adrenalin pumping, they both laughed at the absurdity of two men fighting an army of elephants. They turned and ran.

Their Parthian centurion glared furiously at them as they reassumed their position. But it was not the time or place to punish minor infractions like this. It was enough that hundreds of Indians had been killed with no Parthian casualties at all.

Buoyed up by the combined success of the water channels and the catapults’ volleys, the legionaries’ demeanour was much steadier as they watched the elephants approach. The enemy infantry had finally been rallied by their officers and were marching between the grey beasts, using them as protection from attack.

Romulus took in the Indians’ tactic at a glance. The elephants would try to smash apart the Roman shield wall and then the foot soldiers could pour into the gaps. If that happened, the Forgotten Legion would quickly be overwhelmed. He grimaced. It was vital that they used their long spears as Tarquinius had said.

Whooping loudly, the Indian cavalry broke away from their army and cantered off to the west. There was no point trying to charge through the mass of abandoned chariots and corpses, so the Indian leader had ordered a probing attack around his enemies. Romulus was not worried by this. Thanks to the defensive ditches, any attempt to flank the Forgotten Legion would not work. And he doubted the lightly armed horsemen could break through the reserve cohorts either. At least a thousand of the long spears had been held back to use in this exact scenario.

Romulus shifted from foot to foot, trusting in the soldiers at his back, just as they were depending on him and Brennus. Perhaps if they survived, their status as escaped slaves would not be such a badge of hatred for the other legionaries. In his heart, Romulus doubted that would happen. It seemed that in the eyes of citizens and free men, there was an inescapable stain on the character of a former slave. The knowledge left a sour taste in his mouth. He longed to be accepted for what he was – a good soldier.

Using their short staffs to guide their mounts, the mahouts manoeuvred between the stranded chariots full of corpses. The obstacles slowed up their progress, and it bunched the elephants closely. Together with their enormous size, it made them excellent targets.

‘Loose!’ roared the optio by the ballistae.

More stones flew through the air, striking the elephants on their heads and bodies. Some hit the warriors on their backs, hurling them to the ground. The projectiles were not powerful enough to badly injure the huge beasts, but, better than this, they created fear and confusion. Ignoring their frantic mahouts, many elephants immediately whirled around and stampeded into the distance. Any Indian infantry in their path were trampled underfoot without regard.

A pair began fighting fiercely, battering each other with their iron-tipped tusks in an effort to wound or disable. Another barrage of stones landed; one beast was struck in the eye and also ran away, trumpeting in pain. But the rest, better trained, continued tramping forward.