The prisoners were fed barely enough to survive. Chaos descended each time the guards shoved inside to leave provisions on the ground. Men were reduced to beasts, fighting over stale crusts and brackish water. It was thanks to Tarquinius' increasing stature that the friends ate and drank at all. Helped by Romulus, the Etruscan moved tirelessly among the wounded every day, cleaning wounds and administering herbs from a small leather pouch that he had miraculously saved from their captors. As soldiers became aware of his mystical ability, respect for the Etruscan soared even higher and food was kept back for him. It was through someone like the haruspex that a way might be found out of the hell they were in.

Many of the injured succumbed to dehydration and the bloated corpses were only hauled away by the Parthians if the prisoners carried them to the gate. To prevent disease spreading to the nearby city, the guards had constructed a huge pyre, constantly ablaze to cope with the number of dead. At night its ghostly light revealed thin, hungry faces. The smell of burning flesh was all-pervading, its acrid odour adding to the men's distress.

'Bastards should have executed us,' raged Romulus at dawn on the twelfth day. 'A few weeks and we'll all end up like them.'

More than twenty legionaries lay dead nearby.

'Patience,' counselled Tarquinius. 'The air is moving. Soon we will know more.'

Romulus nodded reluctantly but Felix was enraged at the sight of his comrades' corpses. 'What I'd give for a weapon,' he said, thumping the timbers with frustration.

The little Gaul's action caught the eye of a guard, who waved his spear in a clear gesture to stand back.

'Quiet!' hissed Brennus. He would wait as long as Tarquinius was happy to. 'You don't want to die like that legionary.'

The decomposing figure hanging from the T-shaped wooden structure outside was a brutal example of Parthian discipline. Two days before, a burly veteran of the Sixth had spat at the feet of a guard. He had been dragged outside immediately and fastened to a cross.

With thick iron nails driven through his feet, the soldier had been unable to stand for long. Nor could he hang from his transfixed hands. Shifting from one agonising position to another, the victim was soon screaming. The cruel spectacle had carried on for half the morning. Satisfied that the prisoners had seen enough, the guard had abruptly ended the man's suffering with a spear thrust and had left his body in place to serve as a reminder.

Felix sat down.

The Parthian resumed his patrol around the perimeter.

'We are still alive and that means they have something planned,' said the Etruscan.

'Public execution,' growled Felix. 'That's what the Gauls would do.'

'Not for us ordinary soldiers.'

Romulus remained unconvinced. 'In Rome we'd end up in the arena. Are these savages any different?'

'They have no gladiators, no beast hunts. This is not Italy.' Tarquinius was emphatic. 'Listen!'

The Parthian bells and drums had not stopped since dawn. Since their arrival in Seleucia there had been triumphant noises most days, but this was different. Growing ever louder, the clamour had an ominous feel to it. The temperature had been climbing steadily as the sun rose into the clear blue sky and the sweating soldiers were beginning to feel uneasy.

Brennus got to his feet, looking towards the maze of streets that led into the city. 'It's getting nearer.'

Silence hung over the stockade as the din approached. Dirty, bandaged and sunburnt, the survivors of the Sixth got to their feet one by one as the guards chattered excitedly outside.

'What is it, Tarquinius?' Like many, Felix had realised the Etruscan had knowledge of the Parthians.

Eager for any information, a cluster of men formed around him.

Tarquinius rubbed his chin thoughtfully. 'There has been no formal celebration yet.'

'What about Crassus?' asked Romulus. Since the battle, there had been no sign of their general. No doubt he would play an important part.

The Etruscan was about to answer when a group of fifty unusually tall warriors emerged from the brick archway into the open area before the compound. Clad in chain mail and wearing polished spiked helmets, each bore a heavy spear and round shield. They were followed closely by dozens of Parthians in robes, playing instruments. The procession came to an orderly halt, but the harsh music carried on relentlessly.

More than one man made the sign against evil.

'Elite bodyguards,' muttered Tarquinius. 'King Orodes has decided our fate.'

'You know.' Romulus glanced at the Etruscan, who smiled enigmatically.

He ground his teeth.

'Have you seen something else?' said Brennus.

'I told you before. We are going on a long march to the east.'

Alarmed by the revelation, the soldiers stared fearfully at the haruspex.

'Where Alexander led the greatest army ever seen.' By now, Tarquinius had told many stories of the Greek's legendary march into the unknown, three centuries before.

Most faces dropped even further but Romulus had found the tales fascinating. Anticipation coursed through his veins.

'We may be glad that they passed east.' Tarquinius patted the tiny leather pouch hidden in his waistband which contained the herbs and the ancient map they had seen only once before. Along with his scarab ring and the lituus, it was the only personal possession he had managed to retain after capture. 'One of Alexander's soldiers made this. And it passed into my hands for a reason,' he whispered.

They were interrupted as the newcomers' leader began loudly addressing the guards. Heavy ropes were immediately picked up, the same ones that had been used on the prisoners after the battle. Fear, ever present among the prisoners, rose. When one of the gates was half opened, the legionaries' frightened muttering grew even louder. There had been some security in the confined space. What now?

Flanked by several burly warriors with lowered spears, the captain in charge entered the compound and directed those nearest to walk outside. With great reluctance the soldiers obeyed. As they emerged, ropes were tied around their necks. Soon a long file had formed. Counting carefully, the Parthians inside the stockade gestured at more captives to follow.

One man had endured enough. Clad in the distinctive breastplate of an optio, he had been missed when the officers were removed. As the guard pointed with his spear, the optio deliberately shoved him in the chest.

'What's the fool doing?' hissed Romulus. 'He must know what they'll do.'

Tarquinius regarded him steadily. 'Choosing his own fate. It is something we can all do.'

Romulus remembered Bassius' mercy killings and the two mercenaries who had stayed behind at Carrhae. Self-determination was a powerful concept and he struggled to comprehend it.

A swift order rang out and the sentry drove his spear point deep into the man's belly. He doubled over with a scream, hands clutching the shaft. They watched as the guard knelt and drew a thin-bladed dagger. Two others held the optio's arms. As shrieks of agony rent the air, the Parthian captain glared at the remaining soldiers.

The sentry stood up and swung his arm, throwing something through the air. Two glistening eyeballs, their nerves still dangling, landed nearby and Romulus recoiled in disgust, still astonished that anyone could choose such suffering.

Nobody resisted when the officer motioned again for them to walk outside. Romulus shuffled silently past the optio. Inevitably he found his gaze drawn to the mutilated writhing creature, hands clutching its bloody sockets. The low moans filled him with pity, and he clenched his fists.

'No man should have to endure a fate such as that,' he whispered.