Of all the incidents during the Long March - the strategic shift from Red bases in East China; the Zunyi Conference, where the Party abandoned its Russian advisors' plans for urban warfare in favor of Mao Zedong's uniquely Chinese strategy of a rural uprising; or the Red Army's final arrival at Yan'an, Shaanxi province, after an exhausting struggle across Sichuan's airless, high-altitude Aba grasslands - perhaps none is better known than the battle at the Luding Bridge.

To appreciate what happened in May 1935 you need to cross the mountains into western Sichuan and visit Luding, a tiny township stretched thinly along the Dadu River gorge: it's a spectacular setting, with Daxue Mountain's frosted peaks rising more than 5,000 meters above the sea level and the Dadu's brown waters tearing roughly through the gorge below. The river is spanned by a single 100-meter-long suspension bridge, once the only reliable crossing for hundreds of kilometers in any direction, which was built in 1701 after a blacksmith won a 30,000 tael reward for designing it. Decked in wooden planks, the bridge was originally supported by nine chains, but afternoon winds howling through the gorge made it buckle and twist uncontrollably, so the number of chains was eventually increased to 13 to provide extra stability.

Having failed to cross downstream using boats, the Long Marchers arrived at Luding to find that the local warlord's forces had pulled up the bridge's planking, leaving just the chains intact. But the Red Army soldiers were toughened from their months on the road, besides being well-armed with modern weapons: while one branch of the Communist forces attacked the town, it took just 22 Red Army soldiers to climb hand-over-hand along the chains and defeat the pro-Nationalist forces on the far side, despite coming under heavy rifle and machine-gun fire.