Entwined with the bones of European history is this paradox: everything we are, our culture, our freedoms, our moral universe, is owed in part to the self-sacrificing deaths of men who hated everything we stand for. If the highly civilised Persians had, as seemed likely, rolled over mainland Greece as they rolled over most other cultures, we would not have drama, or philosophy, or epic poetry, in anything like the forms they eventually took. So 300 racist snobs, who ate rancid bean soup and slept with boys, fought and died in 480BC, and showed that Persia could not own them, or the future.
Paul Cartledge's study of Thermopylae, "the battle that changed the world", makes as much of a case for the Spartans as he can, admiring their terse speech and obsession with military training, and habit of killing absolute monarchs in ingenious ways. He also avoids simple dualisms of the sort that are one of Persia's great legacies (when the Greeks called the Persians barbarians, they meant that they were not Greeks, not that they were uncivilised), and he praises Tom Holland's excellent Persian Fire for giving us the other side of the story. What the Spartans fought for was not so much freedom - they had an entire nation of slaves to do their laundry and cook their horrid food - as that autonomy without which freedom has no chance of growing.
Xerxes, Great King of Persia, already ruled many Greeks, and others were his allies; one of his closest advisers was an exiled Spartan king. His father, Darius, had made the mistake of underestimating Greek stubbornness and was beaten by the Athenians at Marathon. Accordingly, Xerxes took no chances: his army included crack troops from all over his empire. But 300 Spartans, and a few hundred others in support, held the main pass into central Greece for three days and inflicted appalling losses before being outflanked and killed. Along with the Athenian destruction of Xerxes' fleet, this knocked the wind out of the invasion, although final withdrawal took months. It was an important battle, and a massive victory for spin; the Spartans obtained a moral high ground in the internecine mess of Greek politics.
Every military obsessive from Victorian headmasters to the Nazis has gone on about them since. The Spartans of Thermopylae are our own death cult, suicide bombers made respectable by antiquity. They fought for Sparta's vile constitution, but their deaths are part of our past.