It is one of the great mysteries that has baffled explorers, archaeologists and anthropologists alike - what was the meaning of the giant Easter Island statues and what role did they play in the demise of this once-complex civilisation?
But since the first non-islanders arrived in the remote archipelago half a millennium ago, another equally profound question has niggled away at the backs of their minds: where did they get those hats?
Now British experts, the first to work on the island since the Edwardian archaeologist Katherine Routledge in 1914, believe they are a step closer to resolving the puzzle of the huge red boulders that sit astride the massive monolithic heads in the world's most remote inhabited place.
Dr Colin Richards from the University of Manchester and Dr Sue Hamilton from University College London have discovered the existence of a road used to transport the outcrops of volcanic rock leading to a previously unstudied "sacred" quarry where the material was mined.
They have also found an axe believed to have been left at the quarry as an offering confirming the site's quasi-religious meaning to the ancient Polynesians.
Dr Hamilton believes the "hats" may have represented a plait or top knot worn by the elite chieftains, who were engaged in a bitter struggle for prestige and power, which was symbolised by the building of ever-taller statues known as moai created in memory of their ancestors.
But while more than 1000 statues have been found on the island, only 70-75 hats have been discovered, suggesting the headgear was an added symbol of power.
As well as weighing several tonnes, the "hats" are carved from a crater full of red scoria, a volcanic pumice whose colour symbolises high birth and status. They may have been later additions to existing statues to boost them beyond their rivals.
"Chieftain society was highly competitive and it has been suggested that they were competing so much that they over-ran their resources," said Dr Hamilton.
It is believed these elite leaders mobilised vast teams of workers to harvest the rock, which was then transported several kilometres on rolling tree trunks to the three-storey-high statues, which were placed on special platforms to enhance their position of grandeur.
Dr Hamilton said: "The quarry is in a secret place which is invisible from other parts of the island and the noise of production would have been contained by the crater. These people lived in a successful and well-organised society - the Easter Island of 500 years ago was a managed living environment."
The academics, who will spend a month each year for the next five years investigating their findings, which include an obsidian adze - an 18cm axe-like tool which was used for squaring up logs or hollowing out timber - believe the first "hats" appeared between 1200 and 1300.
This coincided with a dramatic increase in the size of the statues across the island.
The exact cause of the dramatic decline of Easter Island is hotly debated but it is agreed that it was brought on by a dramatic crisis, possibly as a result of resource depletion, war or disease.
Scientists are battling to keep the indigenous traditions alive.
Each major excavation by the British team has been accompanied by a traditional "umu" ceremony with locals dressing up in white feathers and building ovens out of hot stones to offer cooked offerings to placate the island's spirits.
"We are excavating a living culture so we have to be very careful," said Dr Hamilton. "There are very strict rules about what we can and cannot do and we have to respect them."
Dr Richards added: "It is clear the quarry had a sacred context as well as an industrial one. The Polynesians saw the landscape as a living thing and after they carved the rock, the spirits entered the statues."
* Mysterious isle
Situated 4023km off the coast of Chile.
Named by a Dutch explorer in 1722.
Indigenous name is Rapa Nui.
Annexed by Chile in 1888.
Used by Nasa in the 1960s as an emergency landing site.
Today is home to 3500 Rapanuis.
Attracts 20,000 tourists a year.