‘I need a second in command I can trust,’ Themistocles said. ‘You are that man, if you want it – so your role is as much as I can place on your shoulders, whatever weight you can bear. I need you to command a part of our fleet. You’ll meet your captains and work with them, learning all they know, all they can do.’

‘How many?’ Xanthippus said.

Themistocles looked sideways at him.

‘How many do you want? If you say thirty, it will be a help to me. If you say ninety ships, I’ll give them over to your command, in groups of six. Don’t look so shocked. Cimon is not yet thirty and there are few senior captains who’ll take orders from a youth – even a son of Miltiades. There is no template for a fleet of this size, Xanthippus! If you command ninety, that would take a weight off me, in battle. Think of it as a strategos. No, I need you to! I will decide when and whether to engage, but the sea is wider than any battlefield, far too wide for signals or shouted orders. When the masts come down for battle, we are too low, too close to the water, to see far. I need officers in a tight structure, in command of smaller groups. I need men I can trust completely to take the fight to the enemy.’

With a lurch, their speed slackened almost to nothing. The motion of the sea could be felt once again and right down in the thalamos, the deep hold, Xanthippus could hear men breathing so hard it was like a cry of pain with every exhalation.

‘Speed has a cost, then,’ he said more quietly.

‘It does. The fitness of our men is our greatest resource,’ Themistocles said. He lowered his voice. ‘Though the Persian rowers will have been at sea for months by the time they reach us. They are said to be slaves. Who knows how well they are fed and watered? I expect to be faster and more nimble when the oars are out. I pray to Poseidon and Athena that we are. Those two fought over Athens once. Let them both bless us now, their favourite children!’

He smoothed his hair back with one hand, lighter streaks made gold after so many days at sea.

‘We cannot expect them to collapse before us, Xanthippus. It will be hardest of all on those who labour below. All they know is the work of the oars. We give the orders and set the speed. They have to match it, though their muscles burn and sweat pours. Believe me, the amount of water they drink shows their labour.’ He nodded to the trierarch. ‘Half speed there. Have the rudder men make ready for turns.’

Xanthippus saw how Themistocles was careful to speak directly to the ship’s trierarch, preserving his authority over the crew. It was a delicate balance, with the fellow repeating the same order to the keleustes without a delay.