Xerxes felt cold, though he was sweating and a bead trickled down his cheek. He had brought an army and a fleet greater than any the world had known before, but the Greeks had not given way. They had stood in the pass at Thermopylae, with the sea crashing against the shore – and they had refused to surrender. At sea, they had only grown stronger with every ship they sank, working together, forming great spears and drowning his men … For the first time, he considered the idea that he might not break them, that he might not win. The horror of it sat before him like a chasm and he trembled over its depths. He turned his face to the darkness, ashamed.

Mardonius did not speak again. They waited for the king’s word, his order. That was both the glory and the curse of royal blood. Whatever Xerxes decided, they would do. If he asked Mardonius to take his own life, the general would draw a blade and do as he was told without demur. Their fate was his to command, but Xerxes had not expected his own to be threatened. The idea of Greeks conspiring to keep him in their reach was an axe thumping into his roots, disturbing, frightening. He could only bless the name of Themistocles, who had warned him, honoured him even above his own people. He made his decision.

‘General Mardonius, you have an army of the forty nations: my Immortals, regiments of Lydians, Medes, Egyptians, Assyrians, Persian truebloods … all the peoples of the empire. My elite. Your own sons ride with them. You and they … have earned my trust, in all things.’

Mardonius chose to prostrate himself again, hiding the anguish he felt at the strange tone. He did not know where the young king was heading in that moment, though he feared it. Xerxes spoke almost dreamily. The Greeks had undermined his confidence and it broke the general’s heart, for all he understood it. Mardonius too had witnessed the Spartan last stand at Thermopylae. Until that moment, they had not believed Persian warriors had an equal. What he and Xerxes had witnessed over those few days had shaken them both.

‘Rise up, Mardonius,’ Xerxes commanded. His certainty had returned. ‘I cannot let them break that bridge. So, here is my order. You are in command – of all the army and the fleet. The winter storms will make passage home impossible in just a month. Better for me to go now rather than be … trapped here. Yes, that is my decree. I will return home, to guard the bridge of ships and our peoples there. I will be the royal shield. And when it is over, I will honour you and your sons above all others. Speak with my voice. Bring me victory – and I will give you a city as your own, Mardonius. On my oath, before these witnesses, I will.’