The skulls of scores of young men have been found in a burial pit on the route of a new road in Dorset.

So far 45 skulls, believed to be almost 2,000 years old, have been found, and more may be found as the pit is emptied. Archaeologists have called the discovery extraordinary, saying it could be evidence of a disaster, a mass execution, a battle or possibly an epidemic.

The bones recovered so far are still being examined but most appear to be of young men, and are believed to date back to the late iron age or early Roman period. They may be evidence of a fatal encounter between the invaders and the local population, buried at a site which had ritual significance for thousands of years before they died.

David Score, project manager for Oxford Archaeology, said: "There are lots of different types of burial where skeletons may be aligned along a compass axis or in a crouched position, but to find something like this is just incredible.

"We're still working on carefully recording and recovering all of the skeletons, which will be taken back to our offices in Oxford for detailed analysis, and trying to piece together the extraordinary story behind these remains."

As well as the skulls, the archaeologists found torso and leg bones buried in separate sections of the pit.

"It's very early days, but so far, after a visit to the site by our head of burial services, the skulls appear to be predominantly those of young men," Score said.

"At the moment we don't fully understand how or why the remains have come to be deposited in the pit but it seems highly likely that some kind of catastrophic event such as war, disease or execution has occurred."

The Oxford team completed the main excavation at Ridgeway Hill last year, uncovering a series of earlier burials, including cremated remains, skeletons and a man buried with a dagger under a round barrow. This year they had been monitoring the site as roadworks began, but the discovery a fortnight ago, was a complete surprise.

Construction work has stopped, the site has been fenced off and is under 24-hour security, and Dorset county council has appealed to the public to stay away and let the archaeologists get on with their work.

The pit is on the outskirts of Weymouth, where a new relief road is being built, but stands by one of the oldest roads in Europe, the Ridgeway. The site was used for ritual burials for thousands of years before the young men died: the archaeologists had already found burials from neolithic to Roman times, as well as pottery, animal bones and flint tools.