By the time they reached the top of the tower, Barbad’s old legs were aching, his chest tight.

A heavy door, bound with iron like the outer gate, stood at the head of the stairs.

‘Your food and drink will be brought.’ Naduk gestured them through. ‘Your fetters will be removed.’

The door closed behind the boy and the eunuch. They heard the key turn in the lock.

There were two main rooms: a day chamber and a bedroom beyond. A tiny privy, built into the wall, opened off the living room. The rooms were well furnished: rugs on the floor, hangings on the walls, braziers burning, the furniture almost opulent.

The boy opened the shutters. Fresh masonry showed where iron bars had recently been embedded across the slit window. Sasan looked out.

The cold mountain wind whistled in, made the braziers glow.

Barbad unpacked their meagre possessions: some clothes, slippers, a book of poetry, Sasan’s favourite toy – a stuffed lion. They had not been allowed to bring cosmetics or medicines, or writing materials, nothing sharp. Their belts and laces had been removed. The rooms contained no cutlery; none of the hangings had a sash.

Against all etiquette, Barbad sat on a divan unbidden and considered.

The warden had been courteous. He had used Sasan’s name and title, those of his father as well. The silver fetters would be removed from the prince’s wrists and ankles. Perhaps the future was not without hope. Perhaps the King of Kings would show mercy.

Humanity and pity were the kindly sisters of the virtues. For an individual of quality, if the offence was not heinous, it was not unknown for a King of Kings to order the cloak of the miscreant to be whipped instead of his body. The executioners might cut off the tassels of his headgear, not his ears. They might sever his turban, not his head.

But Shapur was not known for his clemency. At the siege of Arete, the Roman prisoners had been blinded with boiling oil. Barbad had seen a rebel sent back to his city tied to a maimed donkey. The man’s ears, hands and feet had been cut off. At Ctesiphon, a traitor had been tied to a wheel for ten days. In the end his eyes had been gouged out, and molten brass poured in his ears. And then there was the even slower yet more horrible execution by the troughs. Barbad had witnessed that, many years before. That day was not something he wanted to remember, but something he would never forget.