Archaeologists excavating ancient graves in western Sweden have found shards from ceramic vessels made in the Roman Empire, in a find that could challenge assumptions about contacts between people in Sweden and the Romans.

The graves in Stenungsund, around 45 kilometres north of Gothenburg, have been dated to between the years 1 and 300 AD. The remains of burned bones from two people were found, along with the pieces of ceramic.

"There are pieces from four or five vessels in each grave, and we have never previously found so many in Sweden," said Bengt Nordqvist, who is leading the dig for the National Heritage Board (Riksantikvarieämbetet).

"They were possibly made in northern Italy or France. Over in Europe this kind of discovery is normal, but in Sweden it is very unusual."

"The discovery shows that contact between Sweden and the Roman Empire was possibly much greater than we used to believe."

The excavations have been going on for around a month. They are being carried out because of plans to use the ground for football pitches.