The centuries-old mystery surrounding the purpose of Rapa Nui’s famously enigmatic monoliths may be coming closer to resolution. New research suggests the enormous statues were constructed to encourage fertile soil during strenuous times when drought and poor soil conditions made agricultural production challenging.

Researchers from the University of California, Los Angeles, Cotsen Institute of Archaeology and Easter Island Statue Project (EISP) concentrated their work on an excavation site at Rano Raraku, a quarry on the eastern side of the Polynesian island with 95 percent of the Moai statues. Two of 21 Moai discovered upright – one on a pedestal and one buried deep in a hole – were of particular interest as their placement meant they were carefully chosen to remain in the quarry. Intricate engravings on the back of these two statues further solidified this theory. A soil chemical analysis showed evidence of banana, taro, and sweet potato remains, among other things, leading scientists to believe that the quarry may have been a soil-rich site ideal for growing conditions.

“When we got the chemistry results back, I did a double-take,” said Sarah Sherwood, geoarchaeologist and soils specialist, in a statement. “There were really high levels of things that I never would have thought would be there, such as calcium and phosphorous. The soil chemistry showed high levels of elements that are key to plant growth and essential for high yields.”

Not only were the soils likely some of the richest on the island, but the quarry is also home to a rainwater-fed lake that would have made the central area ideal for growing food during times when other regions were suffering from a lack of soil nutrients. Here, indigenous populations appeared to plant multiple crops in the same area to diversify their yield and maintain soil fertility.

“Everywhere else on the island the soil was being quickly worn out, eroding, being leeched of elements that feed plants, but in the quarry, with its constant new influx of small fragments of the bedrock generated by the quarrying process, there is a perfect feedback system of water, natural fertilizer, and nutrients,” added Sherwood.

Rapa Nui, otherwise known as Easter Island, has largely been shrouded in mystery. Located off the coast of Chile, the tiny volcanic island is home to 1,000 Moai statues carved between 1250 and 1500 CE whose origin and purpose remain unknown. Early inhabitants were of Polynesian descent but likely mingled with local South Americans before the ancient society collapsed, perhaps due to an ecological disaster. Scientists have speculated that the locations of the Moai statues helped inhabitants to identify freshwater sources.

“This study radically alters the idea that all standing statues in Rano Raraku were simply awaiting transport out of the quarry,” said Jo Anne Van Tilburg, director of the EISP. “That is, these and probably other upright Moai in Rano Raraku were retained in place to ensure the sacred nature of the quarry itself. The Moai were central to the idea of fertility, and in Rapanui belief, their presence here stimulated agricultural food production.”

Van Tilburg and her team next hope to examine the carved petroglyphs in order to determine whether they too have a significant meaning. The study was published in the Journal of Archeological Science.