Xanthippus walked the long deck with the Spartan navarch, noting every detail, while the rowers slept wrapped in their cloaks, like the pupae of moths in the darkness. There had been no wine to accompany the meal, so he was surprised when Eurybiades produced a skin, pulling the stopper with his teeth and passing it over. It was raw stuff and strong, so that Xanthippus had to wince as he turned away and passed it back.

‘I wanted to ask why you were exiled,’ Eurybiades said. He looked out over the sea as he spoke, then drank deeply from the skin.

‘Did Themistocles not tell you?’ Xanthippus asked.

‘He said you have some foolish system in Athens, where any man can be sent away for no good reason at all. He swore it was true, though I thought it would be … more than that.’

‘It is a guard against tyrants,’ Xanthippus murmured. ‘Though I was not one. Still, I must trust the people – and the gods. There is no other authority in the world.’

‘There is violence,’ Eurybiades said. He drew a knife from his belt, a curved and wicked thing that caught the moonlight. ‘If I hold this knife to your throat now, will you not say whatever I tell you to say? There is authority in that.’

Xanthippus stood still, judging the man.

‘There is some truth in what you say … but even a Spartan sleeps. You cannot keep an entire people in bondage. If it takes a lifetime, or a dozen of them, they will rise up.’

Eurybiades chuckled.

‘The helots in Sparta have been slaves for hundreds of years. Their children are born slaves, their grandchildren serve Sparta in the same way. Believe me when I say authority can be absolute.’

Xanthippus kept his eye on the man as Eurybiades put away his knife and drank from the wineskin once more. Themistocles had been certain they needed the Spartan, with his ships, his crews – and the army on land. Xanthippus felt a desperate need to argue for the Athenian constitution with every part of his strength. Yet he could not. On a Spartan warship, with war coming, he could not.

‘I am a man of Athens, navarch,’ he said. ‘I was sent into exile and I went. I was called home – and I came home. I give my life for Athens – and I will obey.’

‘There. You see to the heart of it. That is all I wished to ask!’ Eurybiades said.

He passed back the skin and Xanthippus drank again, though it seemed more bitter than it had before.

When he was returned to his own ship, he felt exhaustion lying heavily on him. Xanthippus climbed the rope ladder and gave the word of the day to the guard who challenged him.

He wrapped himself in a thick cloak and lay down with dozens of sleeping shapes on the open deck. Xanthippus found himself encouraged as he stared up at the stars. The fleet had spent the day in manoeuvres, practising formations and techniques, from simple mass turns to charges in a wide line, protecting one another’s flanks. Xanthippus understood that one well enough. In the phalanx, a hoplite held his shield to protect the man next to him – and trusted his life to another doing just the same.