It was in 490BC and the Persians (the Man Utd of their day) invaded Greece. The Athenians met them at Marathon, and with the help of a fine pincer movement, drove them back into the sea and slaughtered them. According to Herodotus in his book The Histories there were only 192 Athenian casualties compared with 6,400 of the Persians. Quite a stuffing.
The battle has gone into legend because an Athenian messenger ran 26 miles from Marathon to Athens to announce the great victory to the locals. He died immediately after parting with the news.