There were almost exactly 11,000 Greeks: that's 1,000 men from each of the tribes of Athens, and 1,000 men from nearby Plataea.
The Persians used 600 boats to ferry in troops. The actual number of troops is unknown, but for that number of transport craft it comes to between 30,000 and 100,000 Persians, including a few thousand cavalry.
So the first ratio is that the Greeks were outnumbered somewhere between 3:1 to 9:1, depending what assumptions you want to make about Persian transports.
The next ratio is known with great precision:
203 Greek dead.
6,400 Persian dead.
That's 32 Persian dead for every Greek who fell.
Which isn't bad going when you're not just outnumbered, but also you're the attacking side.
The casualty numbers are known because the Greeks set up a memorial that listed all their fallen. The Persian numbers are known because before the battle the Greeks had promised to the Gods to sacrifice a goat for every enemy they killed. They counted the Persian dead carefully and then discovered they'd killed so many enemies that they couldn't find enough goats. They paid off their debt to the Gods on a yearly instalment plan that took thirteen years to complete.
Despite its vast importance, there's very little agreement about what actually happened. Modern historians can’t even agree on which direction the opposing lines faced, let alone details like whether the Persian cavalry took the field.
One theory goes that the Persians were aligned with their backs to the sea, and the Greeks attacked from inland. Like so:
I'm pretty sure if you gave this problem to any modern military commander, he would instantly place his outnumbered Greeks so that they had to span the shortest possible line. Which would be like this:
|Right. From The Battle of Marathon by Peter Krentz|
You'll notice there's solid land in the top right of one map and a small bay in the other. Most maps put a marsh there. In fact the Greek coastline changes constantly and all three options have been on that spot at one time or another. Nobody really knows what was there when the battle was fought.
The Greeks made the decision to take the fight to the enemy. Each soldier lightened his battle load as much as possible the night before and then they marched out at first light.
The next big point of contention is that Herodotus states, very clearly, that the Greeks marched to within 8 stadia of the enemy, and then they ran in the rest of the way under a hail of arrows.
At the ancient Olympics there was an event in which the competitors ran two lengths of the stadium — two stadia — in soldier’s kit. The men of Marathon ran four times that distance, knowing that at the end they would have to fight for their lives against an enemy many times more numerous.
A lot of modern historians discount that story out of hand, on the grounds that heavy infantry can't run almost a mile and then fight.
The problem is, that the ancient sources are absolutely unanimous that that's what happened. Every written source, every sculptural relief , gives the same picture. And Herodotus, who is often vague on numbers, is absolutely precise on this one. Herodotus also goes out of his way to make the point that everyone dropped as much load as they could, even shedding armour so they could move fast.
Why did they have to run? I think the reason was the Persian cavalry, who could have torn the Greeks apart. Herodotus says the cavalry was there, but once the battle begins he never mentions them. I think the reason is that the Greek plan was to engage the enemy line before the enemy cavalry had time to deploy. With the mountains on one side and the sea on the other, it meant that once the infantry engaged the mounted troops were bottled up behind their own line.
The fact is that modern elite troops could make that run. The counter-argument is that the citizen militia of Athens weren't professional soldiers. Which is true. But what is also true is that we're talking about the most successful citizen army in all history, and those guys in the line knew with utter certainty that they wouldn't live to midday if they didn't cross the field in time.