PALERMO, Italy, Aug. 10 (UPI) -- Archaeologists have discovered an ancient limestone monolith at the bottom of the Mediterranean Sea.
Researchers say the 10,000-year-old stone structure was assembled carved by Mesolithic people who inhabited the string of islands that once dotted the channel between Tunisia and Sicily.
The Stonehenge-style monolith measures 40 feet in length and was found resting some 130 feet beneath the sea's surface. Though it broke in two and rests on its side, researchers say it would have once stood upright, rising more than 40 feet high.
A series of holes weaving through the different parts of the monolith prove that it was man-made. But like Stonehenge, researchers don't know for what purpose it was built.
"The monolith has three regular holes of similar diameter: one that crosses it completely on its top, and another two at two sides of the monolith; there are no reasonable known natural processes that may produce these elements," researchers write in their paper on the discovery, newly published in the Journal of Archaeological Science.
The study was co-authored by Emanuele Lodolo of the National Institute of Oceanography and Zvi Ben-Avraham from Tel Aviv University.
The monolith originally sat upon Pantelleria Vecchia Bank, one of many now-submerged Sicilian Channel islands upon which ancient Mediterranean civilizations thrived. The people of these islands were forced inland as melting glaciers pushed sea levels higher and higher beginning around 9,500 years ago.
"This discovery reveals the technological innovation and development achieved by the Mesolithic inhabitants in the Sicilian Channel region," Lodolo told Discovery News.
"The monolith found, made of a single, large block, required a cutting, extraction, transportation and installation, which undoubtedly reveals important technical skills and great engineering," researchers wrote.
In other words, the kinds of people inhabiting these ancient islands were skilled and technologically advanced, likely participating in trade and making journeys across the seas.
Lodolo says there are surely many more clues as to the nature of these ancient civilizations, just waiting to be discovered on the Mediterranean seabed.