Paris - First run in Athens in 1896 in just under three hours, the marathon has become the classic challenge for thousands of runners around the world every year.
As Kenyan Olympic champion Eliud Kipchoge attempts the previously unthinkable feat of breaking the two-hour barrier Saturday, AFP looks back at other marathon milestones.
The inspiration for the feat is the popular, albeit historically inaccurate myth of Pheidippides, the Greek "hemerodromos" (military runner), who is said to have run from the battlefield of Marathon to Athens in 490 BC to announce victory over the Persians, only to die of exhaustion afterwards.
In spite of the fact the story was invented by the satirist Lucian in the second century AD - around 700 years after the Battle of Marathon - Baron de Coubertin, father of the modern Olympics, championed the romance and bravery of the tale to ignite interest in the 1896 Olympics.
Seventeen runners took part in the first Olympic marathon at the inaugural Games in 1896, starting in Marathon and ending in the Olympic stadium in Athens, a distance of just under 40km - a little short of today's standard 42.195-kilometres (26 miles 385 yards).
The first to cross the finish line was a shepherd and former soldier, Spyridon Louis, who became a national hero when he completed the race in 2.58 despite stopping to quaff a glass of wine halfway through.
Third-place finisher Spyridon Belokas was disqualified after it was discovered that he had completed part of the course in a carriage.
A Greek woman, Stamata Revithi, was denied entry to the race although contemporary reports claim that she successfully completed the course the day after.
Twelve years later at the London Games, tiny Italian Dorando Pietri -- he stood just 1.59 metres -- entered London's White City stadium dehydrated, in agony and drunk with fatigue as he closed in on victory.
He was helped by spectators and half-carried over the line, finishing first in a time of 2.54:46 and then collapsing unconscious.
Pietri was disqualified for being helped and the race awarded to Johnny Hayes, who finished 32secs behind, after an appeal from the American team. Moved by his exploit, Queen Alexandra presented Pietri with a gilded silver cup and he became an international celebrity.
That race, which started in Windsor and ended at White City, was the first time the marathon -- previously around 40km-long -- was run at 42.195km, with an extra 385 yards (352 metres) added to set the finish line in front of the royal box.
This would become fixed as its official distance and Hayes' time of 2.55:18 was the first official world record.
Ethiopia's Abebe Bikila became an international sporting icon at the 1960 Rome Olympics, running barefoot to victory on his way to setting a new world record of 2.15:16 and making history as the first African to win the Olympic marathon.
Bikila twice passed the Obelisk of Axum -- erected opposite the Circus Maximus in 1937 after it was taken from Ethiopia by the Fascist regime -- and raced up an ancient Appian Way lit by Italian soldiers holding torches on his way to finishing at the Arch of Constantine just by the Colosseum.
He was nearly 28 when he won the marathon, which was staged in the late afternoon and evening due to the punishing late summer heat.
The former soldier, and member of the imperial bodyguard of ruler Haile Selassie, retained his title four years later in Tokyo -- he was the first person to win two Olympic marathons - and paved the way for an era of African distance running dominance.
Ever since Stamata Revithi was prevented from running in the 1896 Olympics, women were banned from taking part in marathons, officially for reasons of health and feminity.
But in 1967 a 20-year-old journalism student, Kathrine Switzer, defied the ban and ran in the Boston marathon, becoming the first woman officially to complete the course.
She gained entry by registering as KV Switzer and was issued race number 261. On seeing her during the race, one organiser tried to remove her bib and expel her but was prevented by her coach and her partner, a hammer thrower.
The scene was captured by a photographer and travelled the world, turning Switzer into a feminist icon.
Fired by anger and a desire to show that women could run the distance, Switzer completed the race in 4.20.
The Boston marathon was officially opened to women in 1972 and in 1984 women ran the Olympic marathon for the first time.
Switzer won the New York marathon in 1974 and in 2017, at the age of 70, she returned to Boston. Again wearing bib number 261, she finished in 4.44:31.
On a flat course and with a finish line at the Brandenburg Gate, the Berlin marathon has gained a reputation as the ideal circuit for setting new world records.
Eliud Kipchoge did just that in September 2018 with a lightning quick time of 2.01:39, smashing Dennis Kimetto's previous record by an astonishing 78 seconds.
The Kenyan had taken inspiration from a run he made in May 2017 when he clocked 2.00:25 on a special track at the Monza National Autodrome in Italy.
It was the fastest run over the marathon distance but because of the time trial tactics used it is not recognised by the International Association of Athletics Federations (IAAF).
Kipchoge will try again to break the two-hour barrier in Vienna on Saturday.