As runners from New Zealand and around the world limber up to run 42.195km for the Auckland Marathon on Sunday, some may want to reflect on the ancient origins of the day.
It is 2500 years since the legendary first marathon took place.
In 490BC a momentous clash of civilizations took place near Athens, between an invading Persian army, and a grossly outnumbered force of Greeks - mainly Athenian, but also a small contingent of men from Plataea, a nearby ancient Greek city.
Against all odds, about 10,000 Greeks out-manoeuvred about 25,000 Persians and won a resounding victory.
This was the famous Battle of Marathon, named after the ancient city close to the battlefield. Stories of a long-distance run associated with this battle provide the template for modern-day marathons.
More significant for all of us, marathon runners or not, are the probable consequences if the Athenians and Plataeans had not routed the Persians.
What if the Persians had gone on to crush Athens? Would the famed democracy of fifth-century BC Athens - an idea of which is arguably the most important legacy of Ancient Greece to us today - have been nipped in the bud?
Professor Paul Cartledge, Classics professor at Cambridge University, thinks it would have. At a public lecture in New York he remarked: "that, ultimately for me, is the significance of Marathon". (You can hear the lecture at marathon2500.org).
The legend is usually told as follows. After the Greek victory at Marathon, a runner called Philippides was sent to convey the news to Athens. He ran the entire way, and upon arrival gasped the news: "We won!" but then promptly collapsed from exhaustion and died. The distance would have been about 42 kilometres, the distance of a modern-day marathon.
But did this legendary run really happen? The problem with this story is that ancient writers tell it differently. Stories of a run from Marathon to Athens after the battle are first found in works by Plutarch and Lucian, who were writing 600 years later.
There is, however, some reason to think that similar stories circulated as early as the fourth-century BC.
Disconcertingly, our most important source for the Battle of Marathon, the historian Herodotus, does not mention a run from Marathon to Athens. Instead, he tells of much greater endurance feat. His story makes a 42km run sound like a jog around the block.
Herodotus was writing about 50 years after the events of the battle. He relates that in advance of the clash, a long-distance runner called Philippides (or possibly Pheidippides) was sent by the Athenian generals to run from Athens to Sparta, a distance of around 250km.
Philippides' instructions were to request the Spartans' help against the impending Persian threat. Herodotus says Philippides reached Sparta the day after he left. This is consistent with modern athletes' times in a modern event called the "Spartathlon", which commemorates the run. The winning times for the Spartathlon have ranged from 20.5 hours to more than 26 hours.
Philippides ran in vain. The Spartans explained that they could not come right away, because they were celebrating a religious festival. This has raised many a sceptical eyebrow among modern historians, but it should not be discounted too quickly.
The Spartans did subsequently send their army - and they marched quickly, covering the 250km in three days - but they arrived at the battlefield too late. The Athenians and Plataeans had delayed engagement for a few days while they awaited the Spartan reinforcements, but for reasons which are still debated, they attacked before the Spartans arrived, and won.
On the Plain of Marathon visitors can still see a burial mound which is believed to cover the 192 Athenian citizens who died that day 2500 years ago. A few kilometres away is another burial mound, which some think covers the Plataean dead. The Persian dead are but a memory, preserved in the pages of Herodotus.
Although many of the details of the battle remain unclear and controversial, we know enough to appreciate that the Battle of Marathon was an extraordinarily important event in history.
It was a day when a different outcome would have had far-reaching consequences.
New Zealand, like many countries around the world, has chosen to subscribe to an idea of "democracy" that was still evolving at Athens when the Battle of Marathon took place.
The Athenian democracy was very different from ours today, and it is always worth thinking about what possible forms "democracy" (derived from a Greek word that literally means "people power") might take. Who do present social and political institutions empower? How might other concepts we value, such as equality, justice and liberty, be served better through our democratic systems?
New Zealand is a young country, sometimes said to suffer from "cultural cringe", but we can find strong and deep cultural roots through the study of history, ancient and modern. Auckland marathoners: keep an eye out for the spirit of Philippides beside you as you puff your way across the harbour bridge.
* Dr Jessica Priestley is a Postdoctoral Fellow at Institute of Greece, Rome and the Classical Tradition University of Bristol.