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The ancient Mayan city of Tikal stood proudly at the centre of one of the world's great kingdoms for 1,000 years.
As one of the largest and most important urban centres in the ancient world, it would seem strange if it were to just disappear and become abandoned until rediscovery centuries later, but that's exactly what happened.
In 1853 a gum sapper in Guatemala was out and about minding his business when he unearthed the city of Tikal, which had stood dormant for 1,000 years.
For whatever reason, the Mayans had abandoned it, and many other of their otherwise flourishing cities, in the ninth century AD.
Now, researchers from the University of Cincinnati believe that they have figured it out. It's because the reservoirs in the centre of the city contain toxic and completely undrinkable water in them.
So, the waters that once sustained the ancient civilisation - known to the Mayans as Mutul - is so full of mercury and algae that it would make anyone who consumed it very ill indeed.
That means that, despite the city having stood on that spot since the third century, it had to be abandoned for somewhere with clean drinking water.
The study found: "The conversion of Tikal's central reservoirs from life-sustaining to sickness-inducing places would have both practically and symbolically helped to bring about the abandonment of this magnificent city,"
Because the part of Guatemala that Tikal is situated in is prone to droughts, having a clean reservoir of rainwater would have been vital to the survival of the people living there.
However, a pigment that the Maya used to colour buildings and clay products - amongst other things - appears to have seeped into the reservoirs over the years, creating a dangerous layer of mercury-rich sediment.
The study, which was published in the journal Scientific Reports, asserts that this could have been the final straw for the Mayans living in the city.
David Lentz, the lead author of the study, said: "Archaeologists and anthropologists have been trying to figure out what happened to the Maya for 100 years,
"We found two types of blue-green algae that produce toxic chemicals. The bad thing about these is they're resistant to boiling. It made water in these reservoirs toxic to drink."
Lentz's colleague, Professor Kenneth Tankersley, added: "The water would have looked nasty. It would have tasted nasty.
"There would have been these big blue-green algae blooms. Nobody would have wanted to drink that water."
There you have it, folks.
Not every day you learn the secret - or at least a compelling theory - behind an ancient Mayan mystery, is it?
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