Close behind marched the tightly packed Indian infantry, allowing the Romans to study them properly for the first time. Many men sported cloth turbans, and they wore an incredible variety of garments from loincloths to leather armour and chain mail. Large numbers carried round shields while others carried tall ones fashioned from animal skin. Romulus saw crescent shields similar to those carried by the Scythians, as well as rounded triangular ones. The foot soldiers were armed with spears, long and short swords, axes and knives. Like retiarii in the arena, some even carried tridents. Romulus did not even recognise a number of the weapons: leaf-shaped double-ended blades with a short handle in between, and lengths of thick wood wrapped with bands of iron.

But none of the men struck fear into Romulus’ heart as the elephants did. They were now very near. Terrifyingly, the closest one had a spiked metal ball on a chain attached to the end of its trunk. Romulus could already imagine its destructive power. Suddenly the long spear in his hands, made from Margianian iron and so successful against enemies on horseback, seemed puny.

Following orders, half the legionaries had slung their scuta from their shoulders by their leather carrying straps. Only a two-handed grip on their spears would suffice. To combat the enemy foot soldiers, every second man retained his shield and drew his sword.

Soon the elephant’s musky odour reached their nostrils. It was strong but not unpleasant; Romulus thought he could smell alcohol too. Lines of coloured paint had been drawn around the beast’s eyes, while an ornate silver headdress covering the head completed its exotic and fearsome appearance. Dangling its lethal ball, the prehensile trunk swayed from side to side, its tip scenting the Romans’ alien smell. The mahout shouted and used his goad, forcing the elephant into a shambling run. High above on its back, the warriors readied their bows and spears. Hastily released arrows shot past Romulus, one plunging deep into a legionary’s eye.

His screams did little for the soldiers’ nerves. There were grey faces everywhere now. Men rubbed lucky phallic amulets, cleared their throats nervously and spat on the ground; others whispered prayers to their favourite deities. At least one legionary vomited, his courage frayed to breaking point. The acrid smell of bile mingled with those of the elephant and men’s sweat.

Romulus glanced at Brennus. The Gaul was eyeing him proudly and he ducked his head, embarrassed. A tickling worry began at the back of his mind. Something Tarquinius had said, a long time ago. Could that moment be now?

‘Raise your spears!’ bellowed Aemilius, his nerves still steady. ‘Those at the back, ready pila.’

Wooden shafts clattered together as the front ranks obeyed. Behind them, line after line of right arms swung back, pointing barbed javelin heads upwards. Indian arrows hummed through the air, but the legionaries just had to ignore them. Some struck home, creating small gaps in the line. More shafts followed, accompanied by a volley of stones from the enemy slingers.

Twenty paces separated the two sides.

Screaming blood-curdling battle cries, the Indian infantry broke into a full charge.

A cold sweat broke out on Romulus’ forehead, but his spear tip did not waver. Oddly, Brennus began to laugh, a strange jarring sound coming from deep in his chest. His blue eyes lit up with battle rage; he looked terrifying. Romulus was very glad that the Gaul was fighting with, not against him.

‘Hold steady, lads!’ Aemilius shouted.

To the legionaries’ credit, they did not break.

Blaring with anger from the mahout’s blows, the lead elephant reached the forest of spears. Bending like twigs, half of them simply snapped in two.

Romulus’ vision was entirely filled with flashing metal-tipped tusks, a swinging trunk and the beast’s open, angry mouth. He could see streams of thick, pungent-smelling liquid pouring down the sides of its face, but did not realise their significance. He would find out later that it meant the bull was full of breeding ‘rage’. But all he could do right then was react. And use his spear.

‘Aim at the head!’ screamed Aemilius. ‘Loose javelins!’

A flurry of pila shot up, striking the elephant in the face and wounding the mahout in the right arm. Two of the warriors on its back fell off, injured or killed, but the last continued to fire arrows at the legionaries. Bellowing with rage, the massive creature swung its head and the spiked metal ball spun forward on its chain, sweeping aside more of the long spears as if they were brushwood. As it swung back, the deadly weapon carried a trio of soldiers into the air, crushing the skull of the first and badly injuring the others.

Leaning down towards his mount’s ear, the mahout shouted encouragement.

Around came the ball again, tearing the front ranks apart.

The man next to Romulus had his shoulder smashed into pieces by a glancing blow. With rings of chain mail mashed deep into his flesh, he collapsed in a heap, screaming.

Relieved it had not been him, Romulus stabbed at the elephant’s head. It made no difference at all. The beast’s destructive power was matched by the sheer terror it caused. All the Romans’ efforts were in vain: it was like trying to kill a mythical monster. Even Brennus’ powerful thrusts seemed to have little effect. Romulus was beginning to despair when a lucky javelin took the mahout through the chest. Hurled by a legionary several ranks behind, its pyramidal iron head punched through his ribs. Mortally wounded, he toppled sideways from his position.

‘Now’s our chance!’ cried Romulus, remembering Tarquinius’ advice. ‘Attack it!’

The soldiers’ spirits rallied and a dozen long spears were shoved up into the elephant’s neck and shoulders, penetrating its leather armour. Blood streamed from multiple wounds. Bellowing in pain and no longer guided by the mahout, it turned and pounded back into the Indian ranks, trampling men like ripe fruit.

Before the legionaries could even cheer, the enemy infantry slammed into their lines.

Brennus jumped forward. With a huge slice of his gladius, he took off the head of the first man to reach him.

Frantically, Romulus dropped his spear and unslung his scutum. All around him, his comrades were doing the same, but it was too late to form a complete shield wall.

Short and wiry, the dark-skinned soldiers swarmed into the gaps, thrusting and stabbing.

Plunging his shield boss into a bearded Indian’s face, Romulus felt the man’s cheekbone break against the metal. As he reeled back, Romulus thrust his sword into his unprotected midriff. It was a disabling blow and he ignored the Indian as the blade pulled free. Concentrate on the next enemy, he thought. Stay focused.

Even as he killed another man, Romulus knew that the Indians’ attack was too powerful. He fought on regardless. What else was there to do? Like a machine, he cut and thrust with his gladius, always mindful of the soldiers on either side. Beside him, Brennus bellowed like a lunatic, dispatching every Indian who came near.

At last, thanks to good discipline, the shield wall began to re-form in their section of the line. Without the elephants to back them up, the lightly armed Indian foot soldiers were unable to break the First’s formation. Peering around desperately, Romulus could see that their centre was holding fast, but the cohorts on each side were buckling badly under the pressure.

Then the left flank gave way.

Trumpeting in a combination of triumph and rage, a trio of elephants barged forward, followed by hundreds of baying warriors.

Seeing them, Romulus was swamped by a tide of hopelessness. The end was near. The Indians were simply too many. Even the reserves could not stop this.