The coins were found in a grave in the ground which is believed to be a 1,000 years older than the treasure itself.

The treasure is believed to have been buried there in around 840AD.

The hoard was unearthed when digging began on area identified for a planned development of new apartments.

Beckman-Thoor said that the Vikings travelled widely and that Viking "graffiti" had been found on the walls of Istanbul's Hagia Sophia, a fifth-century former church and mosque which is now a museum.

She said the face value of the coins would be around $8,500 in today's money but that the Vikings would have valued them purely for their weight in silver rather than any nominal value.

It is the first find of its kind in this area of Sweden since the 1880s.