Etched into the surviving art of the Moche, one of South America's most ancient and mysterious civilisations, is a fearsome creature dubbed the Decapitator. Also known as Ai Apaec, the octopus-type figure holds a knife in one hand and a severed head in the other in a graphic rendition of the human sacrifices the Moche practiced in northern Peru 1,500 years ago.

For archaeologists, the horror here is not in Moche iconography, which you see in pottery and mural fragments, but in the hundreds of thousands of trenches scarring the landscape: a warren of man-made pillage. Gangs of looters, known as huaqueros, are ransacking Peru's heritage to illegally sell artefacts to collectors and tourists.

"They come at night to explore the ruins and dig the holes," said Cuba Cruz de Metro, 58, a shopkeeper in the farming village of Galindo. "They don't know the history, they're just looking for bodies and for tombs. They're just looking for things to sell."...