1,000 years on, perils of fake Viking swords are revealed

It must have been an appalling moment when a Viking realised he had paid two cows for a fake designer sword; a clash of blade on blade in battle would have led to his sword, still sharp enough to slice through bone, shattering like glass.

Some Viking swords were among the best ever made, still fearsome weapons after a millennium

bear the maker's name, Ulfberht, in raised letters at the hilt end

Puzzlingly, so do the worst ones, found in fragments on battle sites or in graves

The Vikings would have found it impossible to tell the difference

The difference would have only emerged in use, often fatally

the genuine ones were made from ingots of crucible steel, which the Vikings brought back from furnaces thousands of miles away in modern Afghanistan and Iran

the inferior swords were forged in northern Europe from locally worked iron

genuine Ulfberht swords had a phenomenally high carbon content

11th century the Russians blocked the trade