When Sparta eventually sent an army to force the tyrant Hippias to stand down, they were tempted to stay and rule a competitor city – until every street filled with armed men. The citizens of Athens had been promised self-rule and that is a powerful thing. The Spartan army left, though the incident rankled. Men like the Athenian Cleisthenes thought up rules and tribes and laws – a system of checks and balances and responsibilities, designed so that no one could ever rise to be a tyrant again. It is the birth of democracy, an idea of equality before the law that has endured for two and a half thousand years.

The battle of Marathon that opens this book has a number of gaps in the record. We do not know if King Darius was present. No one knows what happened to the Persian cavalry. Cavalry was a big part of Persian armies at this time – and would be present for the invasion with Xerxes later on. Here, though, the horses are reported and then vanish. It seemed to me that after sacking the seaport of Eretria, the beach at Marathon must have been a handy staging post for an invasion of Athens along the coast. It is only twenty miles away and a reasonable spot for the Persian force that day to regroup, repair and give their horses a chance to run off some seasickness. I’ve assumed the reason the cavalry was not there is because it had gone aboard.

It is true that Xanthippus was present, father of Pericles and husband to Agariste, niece of Cleisthenes. The wonderful Themistocles was there in the centre, to lead the Leontis tribe. Aristides stood with him, leading Antiochis tribe. The ‘polemarch’, or war leader, was Callimachus on the right wing, though Miltiades seems to have been in effective command throughout. Callimachus was killed in the fighting. A statue in his honour was raised on the Acropolis, though it did not survive the Persian invasion.

As a matter of record, the playwright Aeschylus was also there – and saw his brother killed. Miltiades thinned his own centre and then saw it beaten back. His heavy wings then came down on Persian forces and crushed them with long spears and a disciplined phalanx formation. It was as savage as might be expected from men defending their home. The ‘Miltiades helmet’ – presumably the one he wore at Marathon and marked with his name – is at the Archaeological Museum of Olympia, Greece. Though damaged, it is an incredible thing.

I wrote the scene with Miltiades delaying the wing to explain a later event. When Miltiades returned from his failed expedition, having lost men and ships, the great hero of Marathon was badly wounded. In that moment of utter shame and weakness, Xanthippus made his accusation. The trial that followed is hard to explain unless Xanthippus had a personal motive. I wondered if he considered the man a traitor and an enemy, based on something he had seen at Marathon.