‘I have Physician Ganak to help me with pain,’ the king said. ‘He argues with Master Zhou and they take turns to dose me, or burn different woods so I can inhale the smoke.’

Xerxes glanced aside to where the foreigners stood, frowning at them. Both men dropped to the floor immediately. The Indian doctor was white-bearded and ancient-looking, but moved well enough when the crown prince observed him.

A low rhythmic sound, like pieces of wood rubbed together, brought his attention back. Xerxes saw his father was chuckling.

‘I trust them, Xerxes. Do not fear for me. They know what will happen if they let me die.’

‘I wonder if they appreciate the full extent of it,’ Xerxes said.

Both doctors lay on the marble, their hands up around their ears as if cradling their heads. The Chinese master was half the age of the other, but he lay perfectly still, showing good physical discipline. In comparison, the Indian was quivering, expecting death. Xerxes looked away from them.

‘You will grow strong again, father. You must. I am not ready!’

To his surprise, he felt his father’s hand tighten on his own, though it was like being held by a claw.

‘You are. My life has been full and rich, with many blessings. No man lives for ever! Should I fear heaven? Why? It will not be so very different from life as it is now, though without the pain and discomforts of illness. I have prepared you, Xerxes. You are ready to sit this throne today. More, I have prepared my tomb, out in Naqsh-e-Rostam, in the mountains. The carvings are almost complete, yet I live – and I bless your patience. I have asked Our Lord Ahura Mazda for one last campaign. I have known sixty-two summers, Xerxes. With just a few more years, I will gather all our armies, all the host. I will bring a million men and more ships than the world has ever known. I will sail to Greece with them and I will witness the destruction of those who scorned poor Datis, who butchered our people in the surf. The men who showed us only dishonour! The Greeks! The Greeks!’

His voice had risen and his colour deepened as his passion built. Xerxes felt a drop of spittle touch his face, but he did not move to wipe it away.

‘Father …’ he began.

King Darius sat up straighter, anger overriding his physical weakness with a huge effort.

‘Mishar, come to me, complete your duty,’ the king ordered.

The slave ran forward and threw himself down, his golden bracelets clinking on the marble.

‘Master, as you command me.’

The eunuch rose to his feet and leaned in, his lips almost touching the king’s ear. Xerxes felt his father’s rage coming off him like waves of heat. The dark eyes were unblinking as Mishar spoke.

‘Master, I obey. Remember the Greeks,’ he whispered. He stepped away when the king nodded.

‘I remember,’ Darius said.