Every year, between July and October, something extraordinary happens on the banks of Minneriya tank in the heart of Sri Lanka’s Cultural Triangle. As the waters of this ancient reservoir begin to recede with the end of the rains, the exposed lakebed becomes a vast natural grazing ground, and the elephants come. First in small family groups, then in dozens, then in their hundreds, until the shores of the tank are thick with grey silhouettes, the rumble of low vocalisations carrying across the still water at dusk.