The living root bridges get stronger every year they stand, because they are alive. They cross the streams of the Khasi hills in Meghalaya, in northeast India, and they were not built but grown. The pliable aerial roots of a rubber fig are guided over the water along bamboo and palm supports and tended for decades, until they reach the far bank and weave themselves into a deck. Where two roots press against each other long enough, their tissues merge and become one. The roots also answer to being walked on. The ones carrying weight thicken and flatten into load-bearing sections while the idle ones stay round, so the bridge keeps redesigning itself around the traffic instead of wearing out under it. Nobody who starts one is in a hurry, and nobody treats it as finished.
The best known hangs at Nongriat, where two root decks cross the Umshiang one above the other. Getting there is a staircase that drops and drops through the forest; you hear the stream a long time before you see anything, and the last flight sets you down at the mossy mouth of the bridge. Underneath, the water slides over smooth boulders into pools that turn cold and glass-clear once the rains have eased, and you can swim in the very thing the roots were grown to cross. In the monsoon it is a different river. The stream becomes whitewater, the roar fills the gorge, spray comes up through the deck, and the lower span can disappear under the Umshiang altogether. The second deck was grown higher up to escape exactly that. The span gives slightly underfoot as you cross, and along the handrails there are young roots lashed to fresh guides by people alive today. The worst damage done to these trees is not the flood but a knife: the same figs are tapped for latex, and the cuts scar them for good. Above the two decks a third is being drawn across right now, begun by hands that will be old before anyone walks on it.