The Bosnian archaeologist leading the work says the 2,120-foot (650-meter) mound rising above the small town of Visoko resembles pyramid sites in Latin America that he has studied. It would be the first pyramid ever discovered in Europe.
Initial research on the hill, known as Visocica, found that it has perfectly shaped, 45-degree slopes pointing toward the cardinal points and a flat top. Under layers of dirt, workers discovered a paved entrance plateau, entrances to tunnels and large stone blocks that might be part of a pyramid's outer surface.
Satellite photographs and thermal imaging revealed two other, smaller pyramid-shaped hills in the Visoko Valley.
Friday's excavations began with a team of rescue workers from a nearby coal mine being sent into a tunnel believed to be part of an underground network connecting the three hills.
They were followed by archaeologists, geologists and other experts who emerged from the tunnel later to declare that it was certainly human-made.
"This is definitely not a natural formation," said geologist Nadja Nukic.
Weeks of work ahead
The teams descended about 260 meters (yards) into the tunnel but found the rest of the way blocked by a cave-in. The tunnel is thought to be 2.4 miles (3.8 kilometers) long, and the team found two intersections with other tunnels leading off to the left and right.
Other teams began digging 10 shafts at several spots to see if they will run into stone blocks below the slopes of the hill.
The work will continue for about six months at the site just outside Visoko, about 20 miles (30 kilometers) northwest of the capital, Sarajevo. Two experts from Egypt are due to join the team in mid-May.
"We expect the first raw results in about three weeks," said Semir Osmanagic, the Bosnian archaeologist leading the project.
Locals have held many legends about the hill, but Osmanagic, who spent the last 15 years studying the pyramids of Latin America, was the first to suggest that Visocica could be hiding a pyramid.
Anthropologists say the Visoko Valley already offers ample evidence of organized human settlements dating back 7,000 years. The town was Bosnia's capital during the Middle Ages, and German archaeologists working the valley recently found 24,000 Neolithic artifacts just 3 feet (1 meter) below ground.
Osmanagic claims Visocica is a classic example of cultures building on the top of other cultures.
A medieval fortress used by Bosnian kings for two centuries sits on top of the Visocica hill. The fortress was built over a Roman Empire observation post, which was built on the ruins of an Illyrian settlement. The Illyrians inhabited the Balkan peninsula long before Slavic tribes conquered it around A.D. 600.
No pyramids are known in Europe, and there is no evidence any ancient civilization there ever attempted to build one.
Osmanagic believes Visocica is hiding one, though he has no solid theories on how old it is or who might have built it. Osmanagic quickly named the three hills the Pyramids of the Sun, Moon and Dragon.
Tacky souvenirs for tourists
The locals were quick to catch on to the excitement, offering a tacky assortment of pyramid souvenirs for sale to curious visitors.
An unemployed car mechanic from Visoko, Ensad Husic, 36, joined Friday's excavation work in hopes the team will eventually prove Visocica is a pyramid. He sees the project as a job opportunity. "One can already feel the town is busy. I would not be here if I would not believe it is one," he said.
The first tourists are already arriving.
Dirk Wientges, 39, from Rosenheim, Germany, discovered the story about the possible pyramid on the Internet and brought his family over Easter to Visoko.
"We were curious. This is a beautiful country, and I would be happy for it if it would prove this is true. For once one can see Bosnia being mentioned in media in a positive light," he said.
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