The strange ruin is unlike anything found before in the UK and possibly all of Europe, said Steve Clarke, chairman of the Monmouth Archaeological Society, who discovered the structural remains recently in Monmouth, Wales -- a town known for its rich archaeological features.
"It's a real mystery. Whatever it's, there's nothing else like it. It may well be unique," Clarke was quoted as saying by LiveScience.
Clarke and his team unearthed the remnants of three giant timber beams placed alongside one another on a floodplain at the edge of an ancient lake that has long since filled with silt.
After being set into the ground, the pieces of timber decayed, leaving anaerobic (oxygen-free) clay, which formed after silt filled in the timbers' empty slots, Clarke said.
The team initially thought the timber structures were once sleeper beams, or shafts of timber placed in the ground to form the foundations of a house. However, the pieces appear to be too large for that purpose.
While a typical sleeper beam would span about one foot across, these timber beams were over three feet wide and at least 50 feet long.
The archaeologists are still digging and don't yet know how much longer the timbers are. Clarke said the structure's builders appear to have placed whole trees, cut in half lengthwise, into the ground.
"One other thing that is striking that might be relevant is that the timbers seem to be lined up with the middle of the lake," Clarke noted, suggesting that the structures may have been part of a causeway to a crannog, or artificial island, constructed in the middle of the lake.
Though they aren't sure when it was built or even if it came before or after the lake formed, the archaeologists said the structure, at its oldest, could date to the Bronze Age around 4,000 years ago.
Beneath the beams the researchers also found a burnt mound of rock and charcoal fragments, alongside of which they found a hearth and trough. They believe people in the Bronze Age heated stones in a fire and threw them into a filled trough to boil water.