‘But why? Why would you forgive the men who did this, who burned Sardis?’

Darius leaned closer to his son. Though a hundred servants and slaves waited on his slightest whim, though two naked and kohl-eyed women peeped from the curtained litter that adorned his elephant, he was alone still, with his heir.

‘I speak now as a king, Xerxes. Hear me. My word is unbroken because when a man takes the field against my armies, I want him to look in fear on his allies, to wonder if they will desert him, even in the heat of battle. I want him to know, as he knows his own name, that if he surrenders to me, if he takes the taste of dust onto his lips and offers me water from his cupped hands, I will honour him as an ally to the end of the world, without rancour, without vengeance. Because he will be a living example of my mercy. Do you understand?’

Xerxes shook his head a touch, closing his eyes as the wind picked up, easing the great heat of the day. In that moment of silence and peace, he suddenly saw it. His eyes opened and his father smiled to see the gleam in them.

‘Trusting you weakens them all …’ Xerxes said, in something like wonder. ‘It means brother will turn on brother as we approach, friend against friend. But the cost, father? To your honour? You lose vengeance – is it not too high a price to pay?’

‘No. There are forty nations in my empire – Media, Assyria, Lydia, India – by the god that binds, men like silver fish in the ocean, all subject to my throne, my crown. If I were a trickster, a liar, they would have fought much harder to keep me away. Instead, their leaders are given palaces and lands. In their quiet times, they might wonder if they have been conquered at all.’

‘But they have,’ Xerxes said.

His father nodded.

‘Yes. So it is with these cities, this “league of Ionia”. They look to their forefathers the Greeks instead of us. Perhaps they thought I was too far away to care what they did on the very borders of the western seas. They called to Athens for help in their betrayal – and those Greek whores sent ships from Eretria and their hoplite soldiers to roam this coast, to murder and terrorise peoples that are mine. They talk now of throwing off the yoke I have placed on them, of the “outrage” of our rule.’

The king laughed, though there was little humour in it and his eyes remained black and shadowed by his brows.

‘In the destruction of my garrison, the Greeks set the reed roofs of Sardis aflame. It spread like the wind itself until all was consumed, even the temple to Cybele, Great Mother of the World. That is hard to forgive.’

The king stood looking into the distance for a time. His son did not dare interrupt his thoughts. Nor did he resist when his father placed a hand on his shoulder again.