In 1994, archaeologist Ruth Shady Solis stumbled on a strange mound in Peru’s grey lunar desert.

Today, a quarter-century later, the city beneath that mound, Caral, has become one of the keys to understanding humankind’s leap from barbarism to civilisation.

Caral is a prehistoric city founded around 3000 BC in the Supe River valley, some three hours north of Lima. It’s a place of scant aesthetic distinction: parched brown sand flats, a few crumbling pyramids, and little else. Nor is much known of the people who built it, who lack even an agreed-upon name. Yet Caral’s importance is incalculable, for it’s one of only a handful of places on the planet where humans crossed what archaeologists call ‘the great divide’ — where civilisation spontaneously arose out of its opposite.