When he reached a low hill and reined in, his horse began to crop at the wild grasses there. Xerxes took a slow breath and peered into the distance. He brought one hand up and joined thumb to the other fingers, an old scout’s trick that focused his sight further.

Though the distance was great, he could make out the fleets heading to meet one another. The Greeks had brought more ships than he’d known they had. He found himself holding his breath as the fronts met and drove through, as if his hammer had shattered the anvil it struck. The edges of the fleets blurred into one another and he saw ships overturn and plumes of black smoke rise. The battle went on and on until he could not be sure who had the best of it. There was no sound capable of reaching his ears, so that all he heard was the order to halt behind him, with the command rippling back on hundreds of voices until the entire army crashed to a stop. That noise of tramping feet and horses had filled his ears for days. The comparative silence was eerie, especially when he imagined fear and shouts of rage and pain going on, with choking, drowning men slipping slowly down away from the light. He shuddered at the thought.

Xerxes turned when Mardonius rode up with a dozen senior men. The older general would have dismounted to prostrate himself, but Xerxes held up a hand, turning back to the clash of fleets.

‘I cannot tell … whether we are winning,’ Xerxes said.

Mardonius gave a quick grimace, as if he had cracked a tooth on something he ate.

‘The numbers tell the tale, Majesty. Look further back and see how few of our fleet have even reached the battle. The grindstone turns at the front and we have … two or three times as many ships, more. With captains who know you watch them, who know they must drive through the Greeks to join you, to feel your imperial light fall on them once again.’

Xerxes dipped his head, though he was not a fool. He had endured flattery his entire life, from men who wanted favours, or who hoped to influence him or turn away his wrath. He was not immune to it, especially from those of his father’s generation, as Mardonius was. Yet he knew not to trust words alone. He glanced at his general and saw a stiff back and relaxed hands on the pommel of his horse. The man did look confident, Xerxes saw with relief. He realised it was in his gift to inspire others, not least his own general. The young king raised his head and tried to relax his own hands.

‘Lead us then to this pass, Mardonius, this Thermopylae. If it is as narrow as our Thebans claim, we’ll need to push on at speed to keep the fleet on our flank.’

‘As you wish, Majesty.’

Mardonius glanced at the sun, low down on the western hills. ‘It isn’t far now. We will make camp close to where it opens and go through in one push at dawn tomorrow. The fleet will have gone on by then, I have no doubt.’