Every marathon runner knows what it's like to hit the 'wall', the point in a race where legs feel as heavy as lead and the lungs and brain are screaming 'stop'. But for the 650-odd people who will take part in tomorrow's Great Wall Marathon, hitting the wall means traversing 42km of treacherous brickwork along the most celebrated wall of them all.
The route includes a 3km stretch of steps that are so steep just walking up them is difficult. Add in average temperatures of 30 degrees Celsius and it becomes clear why the annual Great Wall Marathon is considered one of the world's toughest races.
'The steps make it very difficult because you can't get into a normal running rhythm,' says Englishman Mike Gratton, who won the London Marathon in 1983, and a bronze medal in the 1982 Commonwealth Games. 'It's not like running up steps in an apartment block, where you can get into a rhythm. On the wall, the steps aren't evenly spaced. You have to jump some of them, or stop and walk.'
Despite that daunting prospect, there's no shortage of people who want to participate. Unlike the unheralded Beijing Marathon, which struggles to compete with the more glamorous races in London, New York, Boston and Berlin, the opportunity to run along China's most famous landmark attracts runners from all around the world.
'The fact that it's a sporting event that takes place on one of the wonders of the world was the main motivation for me to enter,' says Discovery Bay resident Martin Rueegg.
He will be among 1,700 runners who will converge on the Huangyaguan section of the wall, 120km from Tianjin, in the morning. About 1,000 runners will take part in 5km and 10km races. Gratton will be in this group, but his company, 2:09 Events, which is named after his best time for a marathon and organises running holidays, will be sending 50 runners from Britain to take part in the full marathon.