The role of Pheidippides was to run all the way from Athens to Sparta to summon them to the battle at Marathon. He died, hallucinating when he got back after the 120 mile round trip.
It is ofted told he ran the 26 miles from Marathon to Athens to tell of the victory there. He was dead by then. It was the whole 9,000 of the Athenian army which ran, fully armed, back to Athens after the battle, as they realised the Persian cavalry was being sent around by sea to attack the city in their absence. They got there just in time.