Apologies for not writing this up as a proper sketch, at the moment it's more of an idea that needs working on.
OPENING SCENE - we see Pheidippides, the Spartan herald being told that he needs to run from Marathon to Athens to tell them of their victory over the Persians, that this important information must reach the Athenian authorities as soon as possible.
After a few shots of him running through the Greek countryside (with a few obvious references to establish the historical context) then we see shots of him running alongside people dressed as Mickey Mouse, Rhinos etc, he gets stopped and interviewed by Claire Balding which really annoys him as he needs to get to Athens with the news.
The final scene is of him arriving at Athens to be given a foil blanket and a Mars bar, then being shepherded off to get his medal, all the while protesting that he needs to go to the forum to tell them about the Battle.
I kind of see it as a running joke (no pun intended), in that we keep cutting back to see how he's getting on (perhaps at one point we see him running across Tower Bridge with thousands of other people).