Jim Gourley has written a brilliant article for the LAVA magazine called 'Know Your Marathon History - The legendary first road race was longer than you think'.
Those who would like us to believe that marathon running is a great health risk today often love to point out that Pheidippides died after running the first marathon in history. This is just another myth that has become widely accepted through constant repetition. Even the great marathoner Frank Shorter joked: "Why couldn't Pheidippides have died at mile twenty?"
Actually it cannot be confirmed that the story about this Greek messenger is true, or that he even existed. But if he did exist and run, the distance would have been much longer than the modern marathon (42.2 km). In those days running 42 km wasn't such a big deal after all.
If we explore the original historical story as accurately as possible, then it follows that Pheidippides probably ran about 619 km (ie. 14.67 marathons) before he collapsed with exhaustion. He possibly ran this distance in about 100 hours, which would mean an average speed of 6.2 km/hour. He ran solo, without organized support teams like in modern endurance stage races.
Let's take Al Andalus Ultra Trail as an example. In July, this 5-day stage race covers only 220 km - about a third of the distance Pheidippides ran. It's in Spain (with a similar climate to Greece) and considered one of the toughest extreme events. The winner in 2010 took 18 hours 11 minutes to run this distance - excluding the time spent eating, recovering and sleeping each night.
The legend of Pheidippides has very little to do with modern marathon events. Majority of runners who have died during a marathon have had heart anomalies. For example, when Ryan Shay died at 2007 US Olympic Trials, it was reported that his doctor had warned Shay about his heart condition before the race. In ancient times people and their hearts were healthy, because they didn't have junk food.
The risk for sudden death during a marathon has been calculated to be about 0.002% or 1 in 50,000 marathon finishers. Please note that this figure includes runners with diagnosed or unsuspected cardiovascular conditions (most likely coronary artery disease). For healthy and fit runners the risk would be much lower.
The overall risk of dying by living for one year is over 100 times greater than the risk of dying during a marathon.