'Do not presume to judge another,' replied Tarquinius. 'That optio could have walked outside with us. He chose not to.'

'No one can decide another's path,' agreed the Gaul, his tone sombre. Bright in his mind was the image of his uncle, choosing to die to save another. Brennus.

Romulus looked at his friends in turn. Their words resounded inside him.

When fifty soldiers had been assembled, the Parthian commander signalled his guards to stop. As with the sacrifice of the bull, only a few were required as witnesses. Word would spread fast to the remainder.

Led by the cataphracts and musicians, the column got under way. The legionaries shuffled miserably together, urged on by kicks and spear butts.

They passed under the immense archway, which was as big as any Romulus had seen in Italy. But it was the exception rather than the rule. Lined by single-storey mud huts, Seleucia's streets were narrow. Constructed of sun-hardened bricks, the tiny dwellings made up the majority of structures. Just an occasional, plain temple was taller. As in Rome, everything was built very close together, the alleyways between filled with rubbish and human waste. Romulus saw no signs of aqueducts or public toilets. It was a simply built city; the Parthians were clearly not a nation of engineers. They were nomadic desert warriors.

Only the arch and the structure of what must have been King Orodes' residence were impressive enough to exist in Rome. Bare ground extended for some distance around the high, fortified walls of the palace. Towers sat on each corner, with archers patrolling the battlements between. A troop of cataphracts sat on horses beside ornate metal gates, staring impassively as the legionaries filed by. Few could look at the mailed warriors without a shudder of fear.

As he passed, Tarquinius peered through gaps in the metalwork.

'Don't draw their attention!' hissed Brennus.

'They don't care,' replied the Etruscan casually, craning his neck. 'I want a glimpse of the gold Crassus was after. The place is supposed to be dripping with it.'

But one cataphract had seen enough: dropping his lance tip towards Tarquinius, he then forcefully jerked it away.

To Romulus' relief, the haruspex ducked his head and shuffled on.

There was little space for the captives to pass through the waiting crowds. Everyone in Seleucia wanted to revel in the Romans' humiliation. Jeers and shrieks of scorn rang in their ears as they stumbled along. Romulus kept his gaze firmly on the rutted mud beneath his feet. One glance at the brown hate-filled faces had been enough. What was to come would be bad enough without drawing more attention to himself.

Sharp-edged stones and pebbles flew in low arcs, cutting and bruising their bodies. Rotten vegetables – even the contents of chamber pots – rained down. Snot-nosed children in dirty rags darted in and out of the press to kick at the men. One soldier had his cheek raked open by the nails of a thin woman who stepped into his path. When he tried to stop her, a guard clubbed him unconscious. The crone crowed in triumph, spitting on the limp figure. Legionaries in front and behind were forced to carry their comrade.

The filth-covered prisoners were driven through the streets for what seemed an eternity, allowing the stunning victory over Crassus' huge army to be savoured by all. At last they reached a large open area, similar in size to Rome's Campus Martius. The temperature soared as the small amount of shade was left behind. Few dared look up as they were forced towards the centre, away from the jeers and missiles. Guards led the way, viciously beating back those foolish enough to block their path.

Beside a great fire, dozens of Parthians were toiling busily, feeding the hungry flames with logs. An empty stage sat close by. Blows and kicks urged the confused soldiers to stand before it. They formed in weary, beaten lines, wondering, dreading, what was to come. As time passed, more groups arrived, brought from other compounds around the city. Soon there were hundreds of Romans watching – the representatives of ten thousand.

Romulus had decided no one would see him look beaten. If he was about to be executed, it would be a proud end. Brennus seemed content that Tarquinius was not alarmed. Thus he and his mentors were relatively at ease with their fate, in contrast to the half-starved, sunburnt legionaries waiting for death beside them. The awful defeat at Carrhae had shattered their confidence. Heads hung low; quiet sobs racked the weakest. There was even a faint smell of urine as the tension of the situation grew too great for some.

Gradually the mob's abuse died away. Even the drums and bells fell silent. A new sound filled the air, one that instinctively drew attention. Moans of agony were coming from beyond the surrounding crowd.

Dozens of wooden crosses had been erected around the area. From the vertical section of each hung an officer, suspended by ropes holding his forearms to the horizontal crossbar. Periodically the victims pushed up on nailed feet to relieve the pressure on their upper bodies. Then the pain grew too great and they slumped down again, groaning. It was a vicious cycle that would end in total dehydration or suffocation. Death could take days, especially if the victim was physically strong.

The crowd shouted and laughed, their focus drawn away from the other prisoners. Stones flew at the crucified men. Fresh screams rang out when they found targets. Guards prodded the helpless officers with spears, laughing when blood was drawn. Cries of glee filled the air. The brutal spectacle continued in this fashion for some time. The ordinary soldiers watched appalled, each imagining his own fate.

Felix pointed. 'There 's Bassius. Poor bastard.'

Romulus and Brennus stared at the veteran who was hanging nearby, his eyes closed. Despite the agonising ordeal, not a sound was passing the centurion's lips. Never had Bassius' courage been more evident.

Brennus tugged at the cord around his neck. 'I'm going to put him out of his misery.'

'And end up on a cross yourself?' responded Tarquinius.

Romulus swore. The same idea had been in his mind but they could never reach Bassius without being killed first.

'He won't last long,' interjected Felix. 'Crucifixion saps a wounded man's strength very quickly.'

'The Romans taught them how to crucify,' said the Etruscan.

Romulus had no answer. He felt shame and disgust that his own people could have passed on such a barbaric torture. But while slaves and criminals were routinely killed this way in Italy, he had never seen it in such numbers. Then he remembered how Crassus had killed the survivors of Spartacus' army. Rome was as cruel as Parthia.

Brennus spat angrily, preparing to snap his bindings. Images of Conall dying beneath a dozen gladii filled his mind again. Now another valiant man needed to be saved. He had journeyed far enough.

'Your choice, Brennus.' Tarquinius' voice cut in. 'We still have a long road before us.'

The big warrior turned, real anguish in his eyes. 'Bassius is a brave soldier. He saved our lives! And he doesn't deserve to die like an animal.'

'Help him then.'

There was a pause before Brennus sighed heavily. 'Ultan foretold a very long journey. So have you.'

'Bassius will die anyway,' said Tarquinius gently. 'Conall and Brac would have too. There is nothing you could have done to change any of it.'

Brennus' eyes widened. 'You know about my family?'

The Etruscan nodded.

'I have not spoken their names for eight years.'

'Brac was a brave warrior, just like his father. But their time had come.'

The hairs on Romulus' neck rose. He had only ever gleaned hints of the Gaul's past before.

Brennus looked distraught.

'There will be a day when your friends need you.' The Etruscan's voice was deep. 'A time for Brennus to stand and fight. Against terrible odds.'