Two thousand years ago someone cleared the dark stones off this grey plain and let the pale ground show through — a hummingbird, a monkey with a coiled tail, a spider, and hundreds of dead-straight lines running for kilometres. From ground level the shapes make no sense at all, which is why everyone goes up: half an hour in a small plane, or the roadside steel tower on the Panamericana for a look at three of them. What they were for is still an open question.