One of the most gruelling running competitions in the world began on Sunday in Morocco.
By Richard Hamilton
BBC News, Rabat, Morocco
Competitors must run on sand while carrying their own supplies
The Marathon des Sables, or Marathon of the Sands, is a six-day, 240km kilometres (150 miles) endurance race, run across a section of the Sahara desert in southern Morocco.
Previous races have witnessed extraordinary examples of courage and survival.
Unlike the Marrakech marathon, which takes place in January when temperatures are relatively cool, the organisers of the Marathon des Sables seem to wait deliberately until the Sahara gets seriously hot, up to 50 degrees Celsius.
Runners have to trudge over sand dunes and carry their own food and supplies on their backs in a race which is the equivalent of five and a half normal marathons.
The exact route is not revealed to runners until the day before the start to prevent people getting any practice, although it is difficult to imagine who would want to do any more of the course than they need to.
MARATHON DES SABLES
7,000 competitors since 1986
Youngest: 16 years old
Oldest: 78 years old
Women: 14% of competitors
Lahcen Ahansal (Morocco) has won 9 times
About 700 people pay around $5,000 (£2,565) each for the privilege of competing in the race.
The marathon was founded in 1986 by a Frenchman, Patrick Bauer, who had trekked for some 300km (186 miles) through the Algerian Sahara two years earlier and whose desire to share this experience evolved into today's race.
Remarkably only one person has actually died on the course, but the Marathon des Sables has already acquired a catalogue of almost legendary stories of survival.
In 1994, Mauro Prosperi, a police officer from Rome, got lost in a sandstorm and wandered several hundred kilometres off course.
He managed to live for the next nine days on a diet of boiled urine and dead bats. He lost over 13kg (30lbs) during his ordeal but returned to Morocco to race twice more.