Hundreds of years ago, someone took great pains to carve thousands of holes into a long ridge-top strip in the Andean foothills.

Just who built the structure known as Monte Sierpe , and why, has baffled the world since 1933, when the National Geographic Society published Robert Shippee's aerial photographs of the strange site. Now, archaeologists think they know the answer.

An analysis of plant material found inside the holes suggests that it may have initially functioned as a market and later as an accounting system, says a team led by archaeologist Jacob Bongers of the University of Sydney in Australia.

"Why would ancient peoples make over 5,000 holes in the foothills of southern Peru? Were they gardens? Did they capture water? Did they have an agricultural function?" Bongers says

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