The find at Llanbedrgoch on Anglesey includes five bodies, artefacts and the remains of several buildings dating back to the Viking age.

The National Museum of Wales said the site was of international significance.

It is keeping the exact location secret - to prevent possible damage by sightseers.

Other discoveries include a defensive wall and signs that the site could even predate the Early Medieval period.

Clue

The museum said further investigations both at the site and on the bodies and artefacts taken to the National Museum in Cardiff could take many months.

Co-ordinator at the excavation site Mark Redknap said the first clue that there was something there came from objects dug up by enthusiasts with metal detectors.

They have now been drafted into the digging team working on the site.

"The site was brought to our attention by people using metal detectors who have been finding things in some of the fields," he said.

"We are very pleased they did. It is thanks to their prompt reporting that we have a site here which is producing extremely exciting results."

Mr Redknap said the site was oval-shaped and measured100 metres and 130 metres.

It was built over an earlier ditch and contained around six buildings protected by a wall.

Slim evidence

But only the foundations have survived.

"Until the site was discovered there was nothing to see on the ground," added Mr Redknap.

"There are no ground marks, no depressions in the soil, even aerial photography really produced slim evidence.