More than 250 long-distance runners are taking part in one of the world's toughest races - following in the footsteps of a legendary Greek soldier.
The 152-mile (246km) Spartathlon race began at the foot of the Acropolis early on Friday morning.
Runners have just 36 hours to complete the route from Athens to Sparta, which Pheidippides reputedly took in 490BC to get troop reinforcements.
The modern equivalent was started in 1982 by British soldier John Foden.
What is now considered one of the greatest challenges for long-distance runners starts on the last Friday each September at around 0700 (0400 GMT).
It takes participants along highways and dirt tracks and over mountains.
This year I will finish - I promise
This year, the runners have come from around 30 countries across five continents.
"I'm pretty nervous," Samuel Kilpatrick, 41, of Northern Ireland, told the Associated Press news agency before his first attempt at the course. "I'm ready, but nervous sums it up best."
Rina Iwamoto, 37, from Japan - one of 25 women in the race - took part last year, but failed to reach the finishing line. "This year I will finish - I promise," she laughed.
One of the toughest parts of the course is the ascent up the 4,000ft (1,200m) Parthenio Mountain, three-quarters of the way into the race.
"It's really walking and climbing, not running at that point," 50-year-old Michael Brandt, of Germany, told AP.
He has run the race six times, and finished it three times.
The first athlete is expected to enter the main square in Sparta, where the race ends, around 24 hours after setting off.
Each finisher will touch the feet of the statue of the King of Sparta, Leonidas, and will be crowned with an olive wreath.
Greek runner Yiannis Kouros holds the record for the fastest time, completing the course in 1984 in 20 hours, 25 minutes.