A second soldier also chose to stay, but the remaining three were very badly hurt. Too weak to retreat or fight, they had no choice but the last. Muttering briefly with each other, they pulled themselves upright.

'Make it quick, sir,' one said.

Bassius nodded without replying.

A lump formed in Romulus' throat. He had dispatched opponents in the arena but they had rarely been people he 'd known, trained or fought with. This trio of men had been with them since boarding the Achilles, a lifetime ago. After nearly two years of campaigning, Romulus knew the wounded well enough to really grieve their passing.

The centurion firmly gripped each man's hand once. As he moved to stand behind, all three bowed their heads, exposing their necks. They were receiving a soldier's death, an honourable way to die.

Bassius' gladius hissed from the scabbard. He raised it high, holding the hilt in both hands, the razor-sharp tip pointing towards the ground. With a swift motion the centurion stabbed down and cut the spinal cord. Death was instant: the first body crumpled without a murmur. Silently Bassius moved on to the second and third. The mercy killings did not take long; clearly the veteran had performed this grisly task before.

All over the Roman lines, the same act was being repeated by any officers of conscience. But the Parthians had no intention of letting their enemies retreat in good order and another attack began before everyone could be dealt with.

Quickly Bassius organised his new command of exhausted men into a square. With Sido and five other centurions killed, the veteran had assumed control of the regular cohort as well. None of the dazed junior officers questioned the unusual move. Bassius nodded farewell to the Egyptian and his companion. The pair were sitting back to back, swords at the ready.

Eyes full of tears, Romulus could not look back.

'They are brave men.' There was real respect in Tarquinius' face. 'And this is how they have decided to die.'

'Doesn't make it any easier to leave them,' he retorted.

'Stay if you wish,' said the Etruscan. 'That is your choice. Perhaps this is why I could not be sure about all three of us surviving?' His dark eyes were unreadable.

'Now is not the time for you to die,' added Brennus confidently. 'What purpose would it serve?'

Romulus considered the idea, but it seemed pointless. The wounded had freely chosen how they would end their lives and dying with them would prove nothing. There were still many things he wanted to achieve. With a heavy heart, he marched away.

Bassius' incredible willpower held his mixed group together as they left the battlefield behind. To the soldiers' relief, Parthian horsemen did not pursue them for long. Romulus eventually glanced round to see groups of warriors riding in circles, whooping with glee. One waved a familiar shape in the air. It was the ultimate disgrace – a legion's silver eagle, fallen into enemy hands. At the sight, his spirits fell even further.

Beneath the horses' hooves, the huge plain was covered with dead and injured as far as one could see. It was a charnel house. Flies swarmed on to dry staring eyes, gaping mouths, bleeding sword cuts. Nearly fifteen thousand Roman soldiers would never return to Italy. Above them, clouds of vultures now hung on the thermals. The air was filled with the smell of manure, blood and sweat. It had been a bad day for the Republic.

'Lots of men are still alive.'

'We can't help them now,' said Brennus sadly.

'Olenus saw this seventeen years ago,' uttered Tarquinius with some satisfaction. 'He would have liked to see the Romans come to this.'

Romulus was shocked. 'Those are our comrades!'

'What do I care?' the Etruscan replied. 'Rome butchered my people and devastated our cities.'

'But not those men! They did not!'

To his surprise, Tarquinius was nonplussed. 'Wise words,' he admitted. 'May their suffering be short.'

Placated by the compromise from someone who hated all that the Republic stood for, Romulus could still not block out the screams. And there was only one person responsible for it all, he thought angrily.

Crassus.

'Your teacher predicted this battle?' Brennus was amazed.

'And he saw us on a long march to the east,' revealed the Etruscan. 'I had begun to doubt his prediction, but now . . .'

Their eyes widened.

'The gods work in strange ways,' Brennus muttered.

Romulus sighed. There would be no easy return to Rome.

'It is not completely certain.' A faraway look appeared in Tarquinius' eyes, one that Romulus and the Gaul had come to know well. 'The army may yet return to the Euphrates. Much still depends on Crassus.'

'Gods above! Why go that way?' Romulus gestured truculently into the desert. 'Safety. Italy. Everything lies to our west.'

'We would see temples built by Alexander.' For a moment, Tarquinius seemed unaware of their presence. 'And the great city of Barbaricum on the Indian Ocean.'

'Beyond where any Allobroge has ever gone,' whispered Brennus. 'Or will ever go.'

'No one can avoid destiny, Brennus,' said Tarquinius suddenly.

The Gaul went pale beneath his tan.

'Brennus?' Romulus had never seen his friend like this.

'The druid told me that the day I left the village,' he whispered.

'Druids. Haruspices,' announced Tarquinius, clapping the Gaul on the back. 'We are one and the same thing.'

Brennus nodded, full of awe.

He missed the sadness that flitted across Tarquinius' face.

He knows what will happen, thought Romulus. But this was not the time for long conversations. It was time to retreat, or die.

The sun was low in the sky, but hours remained before darkness would offer the exhausted Romans any protection. Slowly the legions limped away from the devastation, harassed by occasional arrows from zealous Parthians. Most warriors remained behind, killing the Roman wounded and looting the dead.

It was a bitter irony. Untold numbers were still dying on the battlefield, giving their comrades the opportunity to escape.

The defeated army straggled north to the walls of Carrhae; at every pace, injured soldiers fell by the wayside. Few had any strength left to help those who collapsed. Anyone not strong enough to march simply perished. Holding his cohort together with roars and screams, Bassius even used the flat of his sword to keep the exhausted men moving. Romulus' respect for him grew even further.

Carrhae was a desert town that existed purely because of its deep subterranean wells. Knowing the settlement would prove useful when the invasion began, Crassus had sent in an occupying force the year before. Its small encampment outside the thick earthen walls was ignored as the thousands of defeated Roman troops reached Carrhae. Men poured through the gates in a great tide, seizing houses and food from the unfortunate residents. The brutal thrusts of gladii instantly ended any resistance.

The majority had to camp outside. A few centurions tried to insist that the temporary ditches and ramparts that traditionally followed a day's march were built. They failed. The soldiers had been through too much to spend three hours digging hot sand. It was all the officers could do to get sentries positioned a few hundred paces into the desert.

The sun had set and with it temperatures dropped sharply, a stiff breeze adding to the chill. Outside the town, those not fortunate enough to have found cover spent the night huddled together in the open. All the tents had been lost with the baggage train. Now the injured began to die of cold, dehydration and fatigue. There was nothing anyone could do.

Romulus and his friends commandeered a miserable mud-walled hut, turning the residents on to the street rather than killing them. Soon they lay sleeping like dead men. Not even the danger of a Parthian attack was enough to keep them awake.