Keen to avoid any confrontation, Valens tried to think of something emollient to say. It was not easy. The image of sharp teeth gnawing at the living flesh of a defenceless man not half a mile away was preying on his mind.

‘Every people consider any practice to which it is accustomed to be admirable and hallowed. To an outsider they may seem ridiculous and incredible, even dreadful and cruel.’

The sentiments were clichéd, but the best Valens could find. They were far from satisfying Hairan.

‘Explanations are not justifications,’ Hairan said. ‘To understand something is not to condone it.’ He had already had several drinks, and now he rounded on Narses. ‘You Persians are a cruel race.’

‘No crueller than any other.’ Narses sounded defensive.

‘Only jackals and wild asses now live where Hatra once stood. Those of my people who were not killed were driven off into captivity.’

‘A great misfortune for you, brother, but such are the laws of war,’ Narses said. ‘Once a battering ram touches the wall of a city, the lives of its inhabitants are forfeit.’

Hairan tugged angrily at his long moustache. ‘After the Sassanid army left, my home was desolate, my family massacred. Once my father died in exile, I was consigned to a lifetime of solitude. What point is there in marrying and having children when all you will do is grieve when a cruel fate takes them, or leave them to mourn you when you die?’

‘Would things have been better if the Romans had taken Hatra? If either of the sieges of the Emperor Septimius Severus had succeeded, your city would have been a desert before you were born. Thanks to the Romans you would never have existed.’ Narses was trying to be conciliatory.

‘Only treachery breached the double walls of Hatra, whose foundations were like sheets of iron.’ Hairan turned to Valens. ‘King Daizan had a daughter. Nadira was the most beautiful woman of her time. Her skin was so delicate you could see right through to the marrow of her bones. She gave the troops wine, and, when they were drunk, opened the gates to the enemy. Shapur had promised to marry her, raise her above his other wives. Instead he commanded a man to mount a wild horse – she was tied by her hair to its tail, and the horse was made to gallop until her body was torn to pieces.’ He looked back at Narses. ‘And you deny cruelty runs deep in Persian blood?’

‘Shapur is one man. Not all Persians are like him.’ Narses spoke abruptly, his patience wearing thin. ‘As you bemoan your fate, remember that I too live in exile.’

‘Desert or betray us, and your road home is open.’

There was silence after Hairan’s words.

Narses hand was on the hilt of his sword.