It's arguably the largest mass sacrifice of children to date. Archaeologists uncovered 269 children, 466 llamas, and 3 adults near the modern-day coastal town of Huanchaco, Peru.

Researchers guess that the mass sacrifice took place during the reign of the Chimú Empire, a pre-Columbian civilization second only to the Incas.

It's not clear why all those children were put to death. But one theory is that sacrificing their young may have been the Chimú's way of placating the angry weather gods.

placating the angry weather gods. Take a look at some of the exclusive images from Huanchaco, featured in the February 2019 issue of National Geographic.

Human sacrifice has been around for centuries — the Maya, Aztecs, and ancient Egyptians killed prisoners of war, volunteers, and slaves over the course of their histories. But child sacrifice, especially mass killings, are incredibly rare.

Previously, evidence of the largest youth sacrifice ever — 42 children — was discovered at Templo Mayor in Tenochtitlán, the ancient Aztec capital, according to National Geographic.

The Chimú people blew that record out of the water.

Ruins of Chan Chan, the capital of the Chimú empire, sit nearby the modern-day town of Huanchaco. In 2011, a local pizza shop owner told Gabriel Prieto, a professor of archaeology from the National University of Trujillo, to check out a nearby vacant lot full of human bones.

Kristin Romey, archaeology editor for National Geographic and author of the magazine's exclusive article on the Chimú findings, told Business Insider that Prieto assumed the shop owner had found a forgotten cemetery. But once Prieto started digging, he realized the bodies were all children, and all 500 years old. Llamas were unearthed too.

Then it came to light that they had all been systematically killed.

Since then, Huanchaquito-Las Llamas, or Las Llamas for short, has been a bustle of activity for archaeologists. "As the excavation seasons progressed, the sheer number of victims was just staggering — no one had ever seen anything like it before," Romey said.

More burials were uncovered on a nearby site in the summer of 2018. The second site, named Pampa la Cruz, yielded more children and llamas to add to the total. The running tally is 269 children, 466 llamas, and 3 adults. It's the largest mass child sacrifice to date in the archaeological record.

In an archaeological saga that began in 2011 and will likely continue in the years to come, experts have tried to understand the what prompted this mass child sacrifice.

Take a look at some photos in the February 2019 issue of National Geographic from the excavation sites, which could help archaeologists shed light on what happened that fateful day some 550 years ago.