No one will be able to deny my brilliance when Seleucia falls, Crassus thought. I will seize power in Rome. Alone.

Cassius Longinus, the boldest of his legates, kicked his heels into his horse 's ribs and came alongside. The soldier's scarred face was concerned.

'Permission to speak, sir?'

'What is it?' Crassus forced himself to be polite. Most of the senior officers did not have nearly as much experience as this man. Longinus was a veteran of many wars, from Gaul to North Africa.

'About Armenia, sir.'

'We have spoken about this already, Legate.'

'I know, sir, but . . .'

'Following Artavasdes' suggestion of marching north to the Armenian mountains and then south again would take three months.' Crassus gripped his reins. 'This way to Seleucia takes only four weeks.'

Longinus paused, considering his words. 'Odd that he refused to accompany us, don't you think? The king of Armenia is a proven loyal subject.'

An awkward silence hung in the air, broken by the distant braying of the mule train. Every officer knew Crassus was not fond of advice.

'He withdrew the instant we mentioned our intended route,' added Longinus.

'These are not Romans we are dealing with!' Displeased, Crassus spat on the sand, the moisture disappearing before it coloured the yellow grains. 'You can't trust them.'

'Precisely, sir,' whispered Longinus. He glared at Ariamnes, the richly dressed Nabataean riding on the edge of the group.

The warrior rode his white mount with arrogant ease, its saddle even more ornate than the general's, the reins braided with gold thread. Above the horse 's head a plume of peacock feathers waved gently in the breeze. Bare-headed, Ariamnes wore a leather coat over his chain mail and his long black hair framed gold earrings dangling from both ears. Richly decorated quivers were strapped to both sides of the saddle and a wickedly curved bow hung over his right shoulder.

'Why believe that perfumed snake? Artavasdes is more worthy than a Nabataean chieftain,' muttered Longinus.

Crassus smiled. 'Ariamnes might have poor taste in scent, but the man has over six thousand cavalry. And he offered to guide us directly to Seleucia. That is the way I want to go.' He waved in the warrior's direction. 'Forget Artavasdes!'

'And water for the men, sir?'

The legates looked up. It had been an unspoken worry among all of them.

Longinus sensed their unease. 'The Tigris flows south out of the Armenian hills, sir. All the way to Seleucia.'

'Enough!' bellowed Crassus. 'The march will not be long. Ariamnes says the Parthians are already running scared. Isn't that right?' he called out.

The Nabataean turned and rode back, his horse prancing across the sand. Nearer the pair, he bowed from the waist. Fixing the general with dark, kohl-rimmed eyes, Ariamnes brought his left hand up to his heart.

'The enemy faded away the instant your legions crossed the river, Excellency.'

'See?' Crassus beamed. 'Nothing can withstand my army!'

Longinus scowled at the brown-skinned warrior. With his oiled ringlets of hair, perfume and curved bow, the man reeked of treachery. And Crassus could not – or would not – see it. Gritting his teeth, the legate trotted off to remonstrate with Publius, who was riding with his Gaulish cavalry on the right flank.

But Caesar's former lieutenant in Gaul was having none of it. He wanted his own part of the victory. 'My father is a hero, Legate,' the stocky noble said jovially. 'He delivered Rome from Spartacus. Saved the Republic.'

And the fool hasn't led an army into battle since, thought Longinus.

'Trust his judgement. He has a nose for gold like I have for a virgin!'

'We do not have enough cavalry to fight the Parthian archers and cataphracts,' insisted Longinus.

'Two thousand Gauls and Iberians and Ariamnes' six thousand horsemen should be more than sufficient.'

'You trust these Nabataeans to fight for us like the Armenians have?'

'What kind of son does not trust his own father?'

His pleas were falling on deaf ears. Wishing the battle-hardened Julius Caesar was in charge instead, Longinus galloped off to the front.

Chapter XXI: Parthia

Since leaving the coast of Asia Minor many months previously, the army's journey had gradually taken it further inland, away from cooling sea breezes. Daytime temperatures climbed steadily, reaching new heights in Syria and Mesopotamia. Initially Crassus had used common sense by following the course of rivers and streams, and the legions had covered most of the march without too much discomfort. But not any more.

Now the brief cool of dawn had faded away, leaving soldiers at the sun's mercy. The yellow orb quickly climbed to fill the entire sky, blasting the ground below. Irrigated fields with their sheltering palm trees grew sparser, then died away completely. Five miles from the Euphrates, all signs of habitation had disappeared. Soon afterwards, the narrow road the legions were following led off between lines of undulating dunes and came to an abrupt end.

The view that awaited them was shocking.

As far as the eye could see, a vast emptiness stretched. It was a burning wasteland and a great sigh of anticipation escaped men's throats. Spirits fell and the cohort's momentum was suddenly stalled by deep sand which was far harder to march in.

'Crassus has lost his mind!' said Brennus furiously. 'Nobody can survive out there.'

'Quite similar to Hades,' commented Tarquinius. 'But if the Greeks did it, we can.'

'Not a living thing. Just sand.' At the limits of Romulus' vision danced a shimmering haze. It was like nothing he had ever seen before.

'What are you waiting for? Sluggards!' screamed Bassius, the phalerae on his chest clinking. 'Forward march! Now!'

The Roman army's formidable discipline prevailed. With a deep intake of breath, the mercenaries entered the desert's oven-like heat. It was not long before the soldiers' feet were burning through the soles of their caligae. Chain mail shirts grew uncomfortably hot to touch. Exposed skin began to burn. Despite strict orders to conserve water, men began taking surreptitious gulps from their gourds.

Romulus was about to do the same when Tarquinius stopped him.

'Save it. The next waterhole is more than a day's march.'

'I'm parched,' he protested.

'The man's right,' added Brennus. 'Stay thirsty.'

Without breaking step, Tarquinius stooped to the ground and picked up three smooth pebbles, passing one to each of them before popping the last in his own mouth. 'Put it under your tongue.'

Brennus raised his eyebrows. 'Have you gone mad?'

'Do as I say,' Tarquinius said with an enigmatic smile.

Both men obeyed and were amazed when moisture instantly developed in their mouths.

'See?' Tarquinius chuckled. 'Stick with me and you'll go far!'

Silently Brennus clapped the Etruscan on the shoulder. He was glad that the soothsayer was full of surprises.

Reassured by his friends' guidance, Romulus strode ahead, full of youthful enthusiasm. The young soldier felt even surer that with Brennus and Tarquinius nearby, little could go wrong. Seleucia would fall in a matter of days, making them rich. Then all he needed was proof of his innocence so he could return to Rome. Quite how that would be achieved was unclear, but he had unfinished business there. Rescuing his mother and Fabiola. Finding Julia. Killing Gemellus.

Starting a slave rebellion.

They had been marching for much of the afternoon when they were alerted by a cry from the front.

'Enemy ahead!'

All eyes turned to the southeast.

Romulus peered at the confusion of sand and rocks but could see nothing.