Unfortunately, Greece was greatly outnumbered. However, because Greece was made up of several small states, Athenian generals sent Phidippides to run 140 miles to Sparta, another polis focused on the art of war, for help. But due to religious beliefs, Sparta could not fight until the full moon, so Phidippides had to run another 140 miles BACK to Athens with the disappointing news. The Athenians marched out to the fields of marathon to battle immediately.
The Athenian Army was outnumbered 4 to 1 but they launched a suprise offensive thrust which at the time appeared suicidal. But by day's end, 6400 Persian bodies lay dead on the field while only 192 Athenians had been killed. The surviving Persians fled to sea and headed south to Athens where they hoped to attack the city before the Greek Army could re-assemble there.
Phidippides was again called upon to run to Athens (26 miles away) to carry the news of the victory and the warning about the approaching Persian ships. Pushing himself past normal limits of human endurance, the reached Athens in perhaps 3 hours, delivered his message and then died shortly thereafter from exhaustion. Sparta and the other Greek polies eventually came to the aid of Athens and they were able to stop the attempt to conquer Greece.