One of the problems that always crops up when reading any ancient document is that nobody can agree on how far away anything is. Unlike today where the standard mile or kilometre are pretty well agreed by everyone, in the ancient world even though you had vast imperial powers sitting over the top of everything, the standard unit of large distances which is the "stade" or "stadium" is more like a serving suggestion.
This problem affects the Iliad, the Odyssey, histories by Livy, Pliny or Herodotus, the Bible, Plutarch's accounts, the list just goes on and on.
I've had enough of this. I am hereby appointing myself as Proconsul Lictor Grand Poohbah and Lord High Everything Else, Rollo Furious Spurious. The judgement that I shall hand down shall be final and although correspondence shall be entered into, the judgement shall only be subject to change if the reason and logic is absolutely phenomenal.
Get it? Got it? Good!
Are you sitting comfortably? Then we'll begin.
In the wars between Greece and Persia, which notably featured King Xerxes who was in charge of 127 provinces (127 provinces) and was madder than Mad Jack McMad (the winner of the Mister Mad Man competition) and who had the ocean flogged and whipped because his floating pontoon bridges didn't work, the Greeks somehow managed to win the Battle of Marathon (or the battle of Snickers if you are reading this after 1990).
The Persians under King Darius and specifically under the command of the General Datis, hideously underestimated the Greeks who had recently mastered the phalanx and proper use of shields. Instead of acting afraid, the Greeks entered full on super saiyan mode and the Persians turned tail and ran away; not coming back for about a decade.
Now according to Herodotus, an Athenian runner named Pheidippides (as opposed to the Athenian tailor Euripides Eumenedes) ran about 140 miles from Athens to Sparta to ask for help but by the time that the Spartans showed up, the Athenian army was already back in town sipping ouzo, veno and metho.
Somewhere down the barrel of history though, probably due to people who take things way to seriously, the actual story of the run to Sparta and the match of the army from Marathon got fused; with some accounts having Pheidippides yell "νενικήκαμεν!" (nenikēkamen) which means "we've won!", before dying of exhaustion.
It stands to reason that this is blatantly idiotic because as anyone who has been to any major sporting fixture knows, when you win something there's a lot of people who all just mill around and begin celebrating. Any runner who was sent with such a message would almost invariably be stopped at every opportunity with people wanting to toast their good health with ouzo, vino and metho.
If we set all that aside, then my judgment which should hopefully make history conform with common sense, is thus:
In the version of events which Herodotus tells us, the army marched 250 stadion from Marathon to Athens. Google maps tells us that the distance from Marathon to Athens is 26.34 miles. 26.34 miles is 46358 yards or as near enough to be 46360 to be good enough and when you divide that by 250 you get 185.44 yards.
I'm willing to accept 185 yards as a standardised standard because going back the other way puts the the distance from Marathon to Athens as 26.27 miles.
Incidentally, the Modern Olympic Marathon is run over 26 miles 385 yards, which is 26.219 miles and the early history of the Olympic Marathon as a sport includes people given strychnine, someone running the wrong way round the Olympic stadium, someone being chased through a field by feral dogs, someone riding in a horse-drawn carriage, and even someone
riding in a car.
I Proconsul Lictor Grand Poohbah and Lord High Everything Else, Rollo Furious Spurious have spoken.
185 yards is your standardised standard Stade.