Plataea sent a thousand hoplites to fight alongside the Athenians at Marathon, and they weren't just showing up for show—they were betting their entire city's future on an Athenian victory.
Here's what makes the Plataean decision so remarkable: if the Persians had won that day, Plataea would have been marked for destruction. They had every logical reason to stay neutral and hope the storm passed them by. Instead, they committed a thousand soldiers to a battle they didn't have to fight. That's not solidarity—that's skin in the game at the highest possible level.
Most Greek cities were hedging their bets in 491 BCE when Persian envoys showed up demanding earth and water as a sign of submission. Plataea didn't hedge. They chose Athens, and they chose to fight.
We tend to remember Marathon as an Athenian victory, period. The Plataeans get a footnote, if they get mentioned at all. But when you look at what actually happened on that plain, you realize Athens couldn't have won without them. A thousand hoplites might not sound like much compared to the Persian forces, but in a hand-to-hand battle where everything comes down to the strength of your line, those thousand soldiers were the difference between victory and disaster.
Herodotus, Histories Book 6, records that the Plataeans sent their entire army to support Athens at Marathon, establishing them as the only Greek city-state to commit forces to the battle.
Herodotus is our oldest and most detailed source for this information, writing his account roughly fifty years after the battle itself.
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