Greece was a dry land, he had come to realise, though he had known deserts where each breath was a contest between life and death. Even so, his regiments had been found gasping before Mardonius refilled the water casks whenever they passed a spring or stream. They had not been able to leave food stores so far south and so they were already on half-rations, with supplies running low. Yet they were almost there. Xerxes and Mardonius and all the senior men had pulled off an extraordinary migration. Over three hundred thousand had marched all the way from Thrace to Greece, around the great arc of the coast. Mardonius had lost no more than eight hundred in that time, to accident, weakness, disease or execution. It was an incredible achievement, brought about by an empire’s wealth and organisation. Xerxes felt the pride of it swell in him.

The young king glanced over his shoulder and saw regiments of ten thousand stretching back and back, with the camp followers and carts bringing up the rear in a great cloud of dust that rose to the horizon. It made him realise the ground was sloping up towards the hills. He rode with the sea on his left-hand side, the great fleet accompanying him, with horses and soldiers ready to snap shut on Athens. They would be the anvil; he the hammer brought down. It was a fine thought.

He saw the mounted scouts raise a hand in warning, pointing to the sea. Xerxes swallowed against a knot of anxiety and kicked his mount to a trot. The path through the mountains took him close to the shore, which pleased him. He had grown used to watching the slow creep of his army while he sat on board the flagship. It was satisfying to mirror the same action on horseback, watching the fleet. That morning, they had kept station with him, heading for the great turn that his Greek allies said would take them south.

He did not trust the men of Thebes, for all they had offered him dust and water and sworn their lives to his care. Despite his father’s wisdom, Xerxes found it hard to accept a people willing to betray their own. He had viewed the queen of Halicarnassus, Artemisia, with similar suspicion – and she had some Persian blood and a closeness of culture that explained some of what she was. Still, the woman disturbed him, with her dark eyes and lingering gaze, so that he was happier for her to remain with the fleet, well away. Power was a dangerous thing for a woman, Xerxes suspected. It corrupted, made her less submissive. There was a reason men imposed obedience on them, from the palaces of kings to the homes of simple labourers. Women were happier with a master. As were men, he considered. A flock needed only one shepherd, after all. With an effort, he put Artemisia from his thoughts.

Xerxes did not know if the Thebans had heard of his maps or knew the extent of the campaign that ended at Marathon. He did not need their knowledge of the land to guide this particular arrow, but it helped to test their loyalty, even so. They had confirmed the existence of the pass that Artemisia said would take his army around the great crags. He would be able to watch the fleet as he marched along the bare shore of Thermopylae, with the great hammer of Persia at his back.