‘What did you say?’ Brutus demanded. No general ever held his troops back like that.

Grinning, the messenger repeated himself. ‘When our lot realised, they stopped and re-formed.’

Brutus swelled with pride. With his first and second lines already committed, Caesar would not have been able to give such a command. With astonishing initiative, his soldiers had shown their top quality by regrouping before the combat began.

A whistling sound filled the air.

Pila, thought Brutus. A volley from each side at twenty or thirty paces and they’ll hit.

Screams and cries began ringing out as the javelins landed. A few moments passed. And then, with a noise like thunder, fifty thousand men smashed into each other.

‘Caesar orders you to prepare yourselves, sir,’ said the messenger, darting off again. ‘All his trust is in you. But do not advance until his flag signals.’

‘Do you hear that, boys?’ Brutus cried to his men. ‘Caesar trusts us completely. And we will repay that confidence. Venus Victrix, Bringer of Victory!’ He roared out the password given to them that morning.

A great sound of approval met his words, swelling as it moved along the cohorts.

Brutus smiled. His legionaries’ morale was high. But that could not rid him of the anxious feeling in the pit of his stomach. Even if Caesar’s hardened veterans in the front two lines won the day against Pompey’s less experienced soldiers, it would all mean nothing when the enemy horse swarmed around their right flank. There were no men on earth who could withstand a cavalry charge from behind. Everything depended on him and his six cohorts. Great Mithras, Brutus thought fervently. Give me courage. Grant me success.

Dismounting, he had a legionary take his mount to the rear. This task was for foot soldiers only, and Brutus wanted to be in the middle of it. He was no officer to lead from the back. Handed a pilum and a spare scutum, he took his place in the front line, nodding encouragingly to his men.

They waited in silence, baking in the hot sun.

An ominous feeling soon took hold of Brutus and he peered into the distance.

Covered by the Gauls and Germans, Caesar’s light infantry were beginning to retreat. Without this protection, they would be run down and killed to a man. But the cavalry’s discipline was good, Brutus saw with relief. Wheeling and turning to confuse the enemy, the tribesmen hurled the last of their spears into the advancing mass of Republican cavalry. Aware that their mounted comrades could not do this for long, the infantry broke into a sprint, towards the side of Caesar’s right flank. They were aiming to pass to the side of Brutus’ position.

The Republican horsemen surged forward, pushing ever harder. Lightly armed with spears and swords, few bore shields or wore armour. They were Thracians, Cappadocians, Galatians and a dozen other nationalities, all vying for the honour of turning the tide in Pompey’s favour. Behind them charged thousands of archers and slingers, the next attack wave.

Brutus chewed a fingernail. This was the most critical point of the battle.

Losing more and more men, still the Gauls and Germans did not break.

The light infantry tore around Brutus’ cohorts, and headed east. If everything went to plan, they would re-form with their mounted comrades in a few moments.

The battered cavalry were perhaps three hundred paces away. Still much too far for an attacking foot soldier to run at a horseman, thought Brutus. Mithras, bring them nearer.

‘Close order!’ He shouted at the nearest centurion. ‘Shields up. Ready pila.’

His order was obeyed at once. Scuta clattered off each other, forming an impenetrable wall. Angled up in the position to throw, his men’s javelins poked forward over the shield wall. Ranks of determined faces peered into the dust cloud before them.

A hundred and fifty paces separated the remnants of the Gauls and Germans from Brutus’ six cohorts. They could hear the excited shouts and cries of the pursuing Republicans. Faces began to grow nervous, and the officers looked to Brutus for orders.

In turn, Brutus glanced anxiously at Caesar’s location. He could just see his general’s red cloak amidst the mass of senior officers and bodyguards. But no damn flag. Come on, Brutus thought, his heart thumping in his chest. Give us the command.

Less than a hundred paces.

Their cavalry were close enough now for Brutus to see the sweat lathered on their tired mounts, the wounded men barely upright in the saddle, the numerous horses without riders. Respect filled him at the heavy sacrifice the tribesmen had made.

Protected by the horses’ height, the six cohorts were still hidden from the enemy. This was precisely Caesar’s purpose.

Seventy paces.

Fifty.

At the last moment, the Gauls and Germans turned their mounts’ heads and rode across the front of the shield wall.

Now, thought Brutus. By Mithras, it has to be now.

Again he looked for the vexillum. This time it was there, a piece of scarlet cloth, urgently bobbing up and down. Typically, Caesar had waited until the last possible moment.

‘At the double,’ Brutus screamed, pointing his javelin. ‘Charge!’

With an inarticulate roar, his men obeyed. Trained relentlessly as new recruits to keep their shields together when running, they presented a fearsome sight to any enemy. Particularly to horsemen, who were never charged by infantry. And for the previous few weeks, Brutus had taught the six cohorts to stab their pila at enemy riders’ eyes and faces. The legionaries were delighted by this novel tactic. As everyone knew, cavalrymen were dandies who thought themselves better than any other soldier.

Shouting at the top of their lungs, they pelted forward, emerging from the dust like grey, avenging ghosts.

The Republican cavalry did not know what had hit them.

As expected, they had driven off Caesar’s horse and light infantry, causing heavy losses. Now the entire enemy rear was exposed and they could break into smaller squadrons, free to ride along it at will. Pompey’s inexperienced soldiers were holding up well, so Caesar’s legions were trapped between a hammer and an anvil. Very soon they would be crushed. Whooping exultantly at the thought of victory, the Republicans trotted forward.

And were met by a shield wall over eleven hundred paces wide.

Stunned, they came to an abrupt halt.

Brutus’ men slammed into them at full tilt. Hundreds of pila stabbed upwards in unison, biting deep into the Republicans’ open mouths, eyes and unarmoured flesh. Plenty of horses were struck too, suffering painful wounds which made them rear up in terror. Keen to cause as much distress to the mounts as possible, the legionaries screamed fierce battle cries. Keeping their scuta locked together, they ripped out the barbed javelin heads and thrust at their enemies again. And again. The shocked cavalrymen quailed before the savage and totally unexpected attack. This was not what was supposed to happen!

The six cohorts managed to move forward a step. Then another.

Brutus was like a hound which has just found the scent. They had to keep the advantage that their surprise had granted them. Considerably outnumbered by the enemy horse, causing panic was their main weapon. ‘Forward,’ he screamed, the veins bulging in his neck. ‘Push forward at will!’

The centurions and junior officers repeated his order.

Seizing the opportunity, groups of legionaries shoved into the gaps between enemy horsemen. Protecting themselves with their scuta, they used their pila to strike terror into the Republicans’ hearts. Here and there, a slashing sword cut down a soldier, but the impetus was all with Brutus’ cohorts. And a few moments later, he saw the most welcome of sights in a battle. Men’s heads turning to the rear. Fearful expressions twisting faces. Cries of alarm. Turn and flee, you whoresons, Brutus thought fiercely. Now.