It is the classic mythic image - Viking warriors tramping across the land in huge horned helmets. The only problem they did not wear them. This depiction was set in stone with the Wagnerian operas. Although, early Roman writers wrote of Northern tribes who wore helmets with various horns or antlers attached, there is cause to think these were the predecessor of the Vikings and most probably one of the groups fitting into the Celtic language and culture matrix. Celtic related images going back to the 8th century B.C, shows horned helmets. A horned god was part of their pantheon.
In the Thames in the 1860's a helmet with horns was found and it is thought they were symbolic offerings or used in some special ritual. The mistake arose from a time when archaeology was largely influenced by a simplistic and linear concept of human development. This thinking labeled everything as either 'primitive' or ' civilized'. People groups who did not adopt the trappings of 'civilization' (huge structures, complex roads, etc.) were labeled 'primitive' and no thought was given to the evidences of advanced societies within more simple social structures. That societies might develop without the need to build castles or houses in stone and might work with nature were not part of the accepted paradigm.