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“The Island of the Sun is an island which has a history going back to 2700 BC,” says Charles Stanish, an archaeologist at the University of South Florida and one of the authors of the new study. “It became a very important pilgrimage destination in the Tiwanaku state by around 650 A.D.”

The city of Tiwanaku may have held as many as 30,000 people at its peak around 800 A.D., according to Stanish. It was complete with elaborate ritual gateways and temples, one of which was virtually reconstructed in 3-D by University of California, Berkeley archaeologist Alexei Vranich.

Coauthor Christophe Delaere of the Centre for Marine Archaeology at Oxford University first detected underwater archaeological deposits more than a decade ago while diving in the lake. In 2013, he and his colleagues returned to Khoa Reef, an underwater area near the Island of the Sun.

The dive team discovered semi-precious carvings like a lapis lazuli puma and a turquoise pendant, as well as valuable thorny oyster shells transported from the warm waters of Ecuador at least 1,250 miles away. Many artifacts also had religious iconography, such as gold medallions depicting a deity with rays exuding from the face and ceramic incense burners shaped like smoking jaguars. The divers also discovered a number of animal bones, the remains of water birds like cormorants and teals as well as frogs, fish and llamas.

Later analysis of the llama bones by Delaere and colleagues found that most of them were unfused, revealing at least one infant and three juvenile individuals. The team also found gold ear tassels and other decorative regalia, likely attached to the llamas before they were sacrificed.

Jose Capriles, an assistant professor in anthropology at Pennsylvania State University and a coauthor of the study, says that no obvious markings show how these young llamas died. But based on evidence from later times, the animals may have been sacrificed by making small incisions around the chest area and pulling the aorta from the heart.

“They could have also drowned them as far as we know,” Capriles says.

Based on the location of the remains, and the discovery of ancient anchors surrounding the reef, the deposits and sacrificial animals are thought to have been thrown from a boat. Adult llamas are fairly large, and transporting them across the often windy, choppy waters of Lake Titicaca would have been logistically challenging. As a result, Vranich says the Tiwanaku may have preferred young llamas due to their ease of transport.

The new artifacts add to a growing body of historical evidence that the Tiwanaku culture experienced a surge of growth and expansion around 800 A.D. “It gives a much stronger idea of when Tiwanaku starts expanding out of its little basin area,” says Vranich, who was not involved in the new study.

While the reasons are still unclear to archaeologists, the culture of Tiwanaku changed vastly during this time. Construction shifted from small, compact buildings to big, open public spaces—possibly to accommodate a population influx. “At this point, Tiwanaku goes viral,” Vranich says.

Radiocarbon dates from the dive artifacts show that they are mostly from this period as well—between 794 and 964 A.D. The ritual deposits in the lake are likely part of a larger pilgrimage around Tiwanaku, Stanish says. The city is about 12 miles from the shores of the lake, separated by about a day’s walk, but travelers would have made a number of stops of ritual importance along the way, taking roughly two weeks to complete the journey. One stop, and perhaps the last, was the Island of the Sun, where more than a dozen archaeological sites dating to the Tiwanaku have been found, including a puma-shaped ceremonial complex on the northwestern end of the island.

“What we’re seeing here is that this ritual offering might have been the tail end [of the pilgrimage],” Vranich says. Similar ritual journeys were picked up again in the Inca period and continue into the present.

Christophe Delaere holding a modern underwater offering deposited near the Island of the Sun in Lake Titicaca. (Image courtesy of Teddy Seguin)

“Colonial Spanish chroniclers documented the vast Inca pilgrimage ceremonial complex built between Copacabana and the Island of the Sun and compiled several legends of underwater deities and offerings,” the authors write in the paper.

After a few centuries during with no major powers controlling the area, the Inca turned the Tiwanaku city site into an important ritual center. The Inca empire may have sought to legitimize its power by linking its legacy with the earlier civilization, both by using some of the same sites and by mimicking their pilgrimage routes.

The researchers also found a number of Inca-era artifacts at the Khoa Reef site, sometimes distinguished by the fact that the Inca often put offerings in stone boxes before lowering them into the water.

Even today, Vranich says, people lower ceramics and other items into the lake as offerings, often between the Island of the Sun and the smaller Island of the Moon nearby—bringing a level of continuity to the sacred place “that has transcended empires.”

The initial significance of the rituals to the Tiwanaku people is less clear. Stanish believes the practice likely played a role in legitimizing the elite class of Tiwanaku culture.

“The emergence and consolidation of the Tiwanaku state was strongly related to the growth and expansion of a religion manifested in a specific iconography and architecture and the rituals that bound them together,” the study authors write, adding that “more than a mere cult in an extreme location,” the rituals at Khoa Reef were likely also performed for theatric visibility, as the Island of the Sun is easy to see from shores of Lake Titicaca.