Following the Nabataeans' hoof prints, two troops of Gauls galloped off in front.

The soldiers marched after them into the empty desert. The horizon remained clear of enemy horsemen and their spirits rose. But as the hours passed without a single cloud to provide respite from the burning sun, the enemy was forgotten as the extreme heat again took its terrible toll on the footsore Romans. Many had drunk all their water the day before and, contrary to Crassus' opinion, the mules had been carrying enough for only some of the soldiers. As thirst levels increased, the rest had no option but to keep walking. The three friends sucked grimly on pebbles, hoarding the remaining liquid in their leather bags as if it was gold.

And then it seemed as if the gods had remembered Crassus' army. Half a dozen Gauls came riding back with news that there was a river ahead. The legions' speed almost doubled, and quickly they made out the typical desert haze that formed over water in the distance.

Patches of reeds on the banks were trampled flat as thirsty mercenaries tramped into the shallow rivulet. Men flopped down headlong in an effort to get cool. But Romulus and his comrades were not allowed long to fill their containers.

'Did I say stop? Or fall out? No!' Bassius roared. 'Keep marching! Bastards!'

Relishing the feeling on his weary muscles, Romulus splashed through the calf-high water. 'A rest would be good,' he muttered, careful not to let the centurion hear.

'Some chance!' Brennus drained his bag, stooping to fill it immediately. 'Drink as much as you can.'

'There'll be no rest for a while.' Tarquinius pointed ahead.

Romulus and the Gaul tore their attention from the refreshing liquid.

All the scouts were riding back at the gallop.

Romulus saw Brennus' hand reaching for his sword. Automatically he did the same, sweat forming on his brow.

The Gauls rushed past the mercenaries, heading directly to Crassus' position. Moments later the bucinae blared with a stridency the men had not heard before.

'Hear that? Enemy in sight! Double time!'

The cohort responded with as much urgency as they could muster, pounding up the river bank, each man hoping the Gauls were wrong.

For the rest of his days, Romulus would remember the sight that greeted him.

On a flat plain in the middle distance sat the Parthian army, a formation nearly a mile across. Their appearance distorted by the haze, thousands of men on horseback waited patiently for the Romans. Huge, brightly coloured banners swirled in the hot air, making them appear even more alien. The noise of pounding drums and clanging bells reached the legions as signallers relayed messages to and fro.

It was an immensely intimidating sight for the exhausted Roman soldiers. Sunburnt faces went pale and oaths were spat. More than one mercenary looked west to the Euphrates and safety.

'Jupiter's balls!' swore Brennus. 'No infantry at all?'

'I told you there would be none,' replied Tarquinius.

There was a short silence. The Gaul visibly braced himself. 'We 'll cope,' he said simply. 'We 'll have to.'

The Etruscan's dark eyes were calm. 'It will all be clear by nightfall.'

They nodded grimly. With a battle to fight, there was little point entertaining fearful thoughts. It was courage and Roman gladii that they needed now.

'What are those?' Romulus pointed at tall humped creatures with long necks and legs, standing behind the enemy lines.

'Camels. The Parthians use them as mules,' explained Tarquinius. 'And they'll be carrying spare arrows, so those bastard archers don't run out. With that many of them, each man will have hundreds of shafts. Real trouble.'

'Because our damn shields are practically useless,' said Brennus, thumping his scutum.

The Etruscan nodded. 'The warriors train with those composite bows every day, my friend. Remember what they did yesterday.'

'But we are free men now.' Brennus clapped Romulus on the shoulder. 'If the gods will it, we shall die together – with our swords in our hands and the sun on our faces. Better than in the arena for that bastard Memor.'

'True.' Romulus met the Gaul's gaze squarely. Mention of the lanista made him remember Cotta's lessons. 'Spartacus wouldn't have worried about facing the Parthians,' he said. 'He always had plenty of horsemen.'

'That Thracian had far more ability than Crassus,' agreed Tarquinius. 'He only got beaten because Crixus, his second-in-command, wouldn't leave Italy. Spartacus would never have led his men into a mess like this.'

Romulus sank into a reverie, imagining himself in charge of the army, Tarquinius and Brennus by his side. Keeping the cavalry on the wings would be the most urgent task, to prevent the legions being outflanked while they formed up. Then the centre could make a tactical withdrawal as the Parthians attacked, allowing the cavalry to enfold the enemy. It was how Hannibal had won so many of his battles against Rome.

Tarquinius regarded him keenly. 'Crassus will not think of trying Carthaginian tactics. The fool thinks all we have to do is advance and the Parthians will flee.'

Romulus was stunned. 'Men like you two should be in charge,' he blurted.

Tarquinius inclined his head. 'And you, Romulus.'

He flushed with delight.

'We 'd do a better job than Crassus,' chuckled Brennus.

'That would not be difficult.' Tarquinius squinted at the Parthians, counting under his breath.

Bassius ordered his men to take up a defensive position on the ridge. One cohort could do little but wait for the rest of the army to catch up. Not a man moved from the Parthian force. Their trap sprung, the enemy was content to let the Romans take up battle formation.

'Shows how confident their leader is. They could be riding in and showering us with arrows.'

'Maybe he wants to fight Crassus in single combat!' joked the Gaul. 'We could put our feet up and watch.'

'It'll be common soldiers bleeding today,' said Tarquinius. 'Not leaders.'

Reconciling himself to his fate, Brennus shrugged his massive shoulders. 'Lanistae. Generals. Whoever. They give the orders. Men like us die.'

Keeping the Etruscan's reassuring words uppermost in his mind, Romulus prayed to Jupiter, his guide since childhood.

You did not need to be a soothsayer to know that thousands would die in the forthcoming battle.

And possibly one of them.

'Where is Ariamnes?' Crassus sat bolt upright in the saddle, his face pinched with anger.

Nobody answered.

There had been no sign of the Nabataeans since dawn. With the full Parthian army in sight, it was obvious that the Romans' erstwhile ally would not be returning.

Ariamnes was a traitor.

'Son of a whore! I will have him disembowelled. Then crucified.'

Longinus tactfully cleared his throat. 'What are your orders, sir?'

Crassus glared at him, but, unwilling to acknowledge any mistakes, his eyes dropped away. 'Cavalry on the wings. Cohorts in one square formation,' the general blustered, picking the boldest tactic he could think of. 'That rabble will take one look at us and flee.'

The grizzled legate gasped. 'And leave gaps between the units?'

'Those are my orders. Is that clear?' said Crassus, bunching his jaw. Although he could immediately see what Longinus meant, his monumental pride was still smarting at the exposure of Ariamnes' treachery. 'This way their greater numbers of horse cannot flank us.'

'Yes, but it also allows those bastards to ride between us,' replied Longinus, expecting his fellow officers to voice their support. None was forthcoming. The legate glared at them, then continued undeterred. 'Sir, solid lines would be better. Then only a small number of men could be attacked at one time.'

Crassus' eyes bulged. 'Are you questioning my orders again?'