''I was sure we would know after a couple years. That's how it usually goes with a dig, but these are the most puzzling thing I've come across in the eastern United States,'' said Mr. Trento, who studied at Oxford, worked for the National Geographic Society and excavated ancient megaliths all over the world.

He theorizes that the chambers were built by American Indians, all conforming to a similar style.

''They're not made by Celts or aliens,'' he said. ''It's actually more interesting than that. You can trace every bit of non-Indian architecture in this country to models in Europe, everything from stone walls to barns. But there is nothing like these chambers in Europe. They are a homegrown, vernacular piece of native architecture. And after all these years, no one has any idea what they are.

''I find it astonishing that we have these incredible pieces of architecture and nobody is looking at them.''

He said that fantastic theories keep away serious archaeologists.

''It's the kiss of death academically,'' he said. ''Tenured N.Y.U. and Harvard professors are not going to study places that have all these loopy people offering fringe archaeological theories on them.''

He added: ''It is so extraordinarily unusual that there are no artifacts there. I've looked at sites around the world, and there's always something left behind, but these have been literally swept clean.

''They're part of our history, and if you're going to start bulldozing them to build housing developments, you're stupid.''