With the grim count from this and a second site found nearby already adding up to 269 bodies, archaeologists now believe the harrowing discovery at what once was Chan Chan, the capital city of the ancient Chimu civilisation, is the biggest child sacrifice site ever found.

And they also found three adults sacrificed with them, two women who are believed to have wrapped the ᴅᴇᴀᴅ children in shrouds and buried them, and a man whose unusually robust build has led archaeologists to wonder if he was the executioner.

Work on excavating the mᴀss burial site now called Huanchaquito-Las Llamas, in Peru’s northern Pacific coast, first started in 2011, when 40 young victims and 74 llamas were initially uncovered.

Until then, the world’s largest known child sacrifice site was at Templo Mayor in the Aztec capital of Tenochтιтlan, now Mexico City, where 42 children were slain in the 15th century.

They lived in a strip of desert, 20 to 100 miles wide, between the Pacific and the Andes, and unlike the Inca, worshipped the moon, believing it to be more powerful than the sun.

Gabriel Prieto, a professor of archeology form the National University of Trujillo, was the first at the Huanchaquito excavation, near the modern Peruvian city of Trujillo, and the expert on Chimu culture soon realised that it was more than just a mᴀss ancient burial site.

The children were all interred in unusual positions, prone on their backs or curled on their sides instead of sitting upright, as was customary.

The bodies also lacked the ornaments, pottery and other grave goods commonly found in Chimu burials, instead surrounded by young llamas and possibly also alpacas.

Many of the children and animals had visible cut marks across their sternum and ribs, while many of the children were daubed with a bright red pigment made from cinnabar – most likely a part of the sacrificial ritual.

The llamas were all younger than 18 months and were all buried facing towards the Andes mountains.

Forensic expert John Verano, who has decades of experience examining ritual violence in the Andes, confirmed that the children and animals were killed in the same way – with a horizontal cut across the chest, probably followed by removal of the heart.

He said: “Until now, we had no idea that the Chimu did anything like that. It’s the luck of archeology.”

With much of what happened already established, investigations turned to perhaps the most important question of all – why?

One major clue found by the archaeologists is a thick layer of ancient, dried mud in which the sacrifice victims were buried.

The mud could have been caused by heavy rains which, on the arid coast of northern Peru, “such rains usually only come with El Nino”, according to Gabriel Prieto.

Experts agree that extreme weather typical of El Nino – higher sea temperatures, severe rain and flooding – would have wreaked havoc on the Chimu’s irrigations systems and coastal fisheries, and even shaken the political and economic stability of the kingdom.

Bioarchaeologist Haagen Klaus suggested the children may have been sacrificed when sacrificing adults did nothing to ward off the adverse climate events.

He said: “People sacrifice that which is of most and greatest value to them. They may have seen that [adult sacrifice] was ineffective. The rains kept coming. Maybe there was a need for a new type of sacrificial victim.”

How the children were chosen for their terrible fate, however, remains a mystery.

Scientific studies show that those killed at Huanchaquito were both boys and girls, all of whom appear to have been well cared for, with little sign of malnutrition and disease.