They've fascinated us for centuries, and scientists may have found an explanation.
No, I'm not talking about UFOs. I am, of course, talking about the iconic figureheads on Easter Island, located in Polynesia, Chile.
These stone heads have been a figure of intrigue for scientists around the world.
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And for people who have watched Night At The Museum, they are synonymous with chewing gum.
Believed to have been carved between 1300 and the 1600s, the volcanic stone figures are called moai in the island’s native Polynesian language.
For years, the reason behind their exact location had evaded explanation. It was understood that they had been built to honour the island's chiefs, but their placement wasn't clear.
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But now, archaeologists think they have cracked the case.
A large portion of the statues were situated along the coast of the Pacific island (known as Rapa Nui).
Researchers from New York's Binghamton University went to the island to investigate. And the conclusion they landed on?
It was all to do with water.
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They found that only a small amount of freshwater was naturally available on the remote island.
Therefore, the residents of Rapa Nui would have been dependent on groundwater discharge hundreds of years ago.
Groundwater discharge is created from underwater aquifers - layers of rock or sediment containing water. When they reach a certain saturation point, the water inside flows out of the ground.
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This allows humans to have drinkable freshwater from wherever it emerges on the coast - because the salt concentration is low enough to allow for safe consumption.
Carl Lip, an anthropologist at Binghamton University, explained: "The [island’s] porous volcanic soils quickly absorb rain, resulting in a lack of streams and rivers.
"Fortunately, water beneath the ground flows downhill and ultimately exits the ground directly at the point at which the porous subterranean rock meets the ocean.
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"When tides are low, this results in the flow of freshwater directly into the sea. Humans can thus take advantage of these sources of freshwater by capturing the water at these points."
Through measuring the percentage of salt in coastal waters, the research team found a correlation between the freshwater supplies and the placement of the statues.
"Now that we know more about the location of freshwater [...] the location of these monuments and other features makes tremendous sense," Lipo concluded. "They are positioned where freshwater is immediately available."
Accounts from the first Europeans who came across the island describe natives drinking seawater.
To the Dutch explorers of the time, this behaviour was incomprehensible. But with the benefit of hindsight, we now understand that they were drinking brackish water - a mix of fresh water with a small amount of saltwater.
Topics: World News, Science
Ben Thompson