VISOKO, Bosnia and Herzegovina — Semir Osmanagic stopped to shake hands and have his photograph taken with a group of mud-flecked Bosnian villagers, pickaxes in hand, on a steep hillside above this small medieval trading town on a bend of the Bosna River. They have dug away four feet of roots and clay to expose slanted slabs of sedimentary stone.

"Look at that megalith, it's got to weigh 40 tons," Mr. Osmanagic said eagerly, pointing to one of the roughly rectangular-shaped stones. "After so many thousands of years, it is amazing that they are still here."

Mr. Osmanagic, an amateur archaeologist, is convinced that he has discovered a huge ancient pyramid that will rewrite the history of Europe — not to mention that of Bosnia, a country suffering from war recriminations, political divisions and sunken pride. Anthropological genetics, he said, has proved that Bosnia is "the second oldest oasis of life in Europe," and the pyramid proves Bosnia is a source of civilization on the Continent.

"It's not just any pyramid," he said from beneath his flat-crowned Navajo hat, which has led the local press to liken him to Indiana Jones. "It's the biggest pyramid in the world."

Archaeologists and historians inside and outside Bosnia are appalled, insisting it is simply a peculiarly symmetrical bit of geology.