From the fate of its once vibrant population to the origins of its moai statues, Easter Island is rife with mystery. As Ars Technica reports, a team of scientists may have answered one question related to the famous heads located on the island off the coast of Chile: Why were they placed in some spots on the island and not others?

According to their study in the journal PLOS One, ancient islanders positioned the moai around precious sources of fresh water. This theory may seem confusing if you're familiar with the island's layout: Almost all of the stone artifacts are located along the coast.

But the study authors write that the statues are markers for hidden water sources. On Easter Island, and other volcanic islands, volcanic tubes carry fresh water from underground into the ocean, creating patches of drinkable water surrounded by the salty sea. Fresh water is a limited resource on the island, and its inhabitants likely depended on these water pockets to survive.

When researchers pinpointed these off-shore water sources, they found either moai statues or the platforms that were used to hold them next to each site. And this wasn't a result of islanders placing moai randomly along the coast: Further analysis revealed that the presence of a freshwater patch was the strongest indicator of where an Easter Island head would be.

Easter Island's scant natural resources are part of the mystery that surrounds its ancient people. At its peak, the Easter Island may have sustained a population of 17,500, and the complex social structure of its inhabitants enabled them to achieve great things, such as carving and transporting 81-ton statues around the island. Though we now have an idea of why the moai ended up where they did, the question of how they got there is still up for debate.

[h/t Ars Technica]