If you begin at the ocean, following Lima’s Avenida Javier Prado going east, past the residential districts of San Isidro and Magdalena, through the traffic-choked intersection with the Via Expresa, past the newly-inaugurated National Library and into the wealthy district of La Molina, past El Jockey, Peru’s first American-style shopping mall, alongside the University of Lima with its glittering tower, and beyond it, to the foot of the hill where the avenue seems to dead-end, there, on the other side of an underused soccer stadium grandiosely named El Monumental, the road shrinks from six lanes to only two—and here you will find a rather unimpressive Inca structure, or the remains of one, riddled with bullet holes.

It’s easy to miss. The structure is just a squat, thick-walled adobe windbreak, much of it crumbled, all of it coated in the same grayish yellow dust that the hills surrounding Lima seem to emanate. It blends seamlessly into the mountainside that hovers over it. There is a better-preserved temple not far away, not as easily visible from the avenue, and together with the hill itself, the entire archaeological area is known as Puruchuco. I went for a visit in July with a local archaeologist, Guillermo Cock, whose macabre discovery in the vicinity had been reported in newspapers all over the world. Here, in Puruchuco, in the outskirts of the Peruvian capital, his team of researchers had found the first confirmed gunshot victim of the Americas: a man’s skull, its parietal bone neatly perforated by a single round hole less than an inch in diameter.

Initially, Cock confessed to me, he didn’t think much of it. His first thought was simple: a stray bullet had found its way into an old skull. When this part of Lima was much less densely inhabited—there are now nearly half a million residents in the immense district of Ate-Vitarte—the area was an ad hoc firing range, hence the bullet holes adorning the otherwise forgotten and obscure Inca ruin...