Vikings did not wear horned helmets. That look comes from a 19th-century opera.

The Viking Age lasted roughly from the late 700s to the mid 1000s. Archaeologists have excavated many graves and settlements from that time, yet the only nearly complete Viking helmet ever found, from Gjermundbu in Norway, is a rounded iron cap with a guard around the eyes and nose. It has no horns. Horns would also have been impractical in battle, giving an enemy something to grab or strike.

So where did the horns come from? In the nineteenth century, artists and writers in Scandinavia and Germany were romanticising the Norse past. When Wagner's Ring cycle premiered at Bayreuth in 1876, costume designer Carl Emil Doepler gave some characters horned and winged helmets. The look caught on in paintings, illustrations and later films.

Many Viking warriors probably did not own a metal helmet at all, since iron was expensive.

The Gjermundbu helmet was discovered in 1943 on a farm in Buskerud, Norway, in a tenth century burial. It is the best preserved Viking Age helmet known, and fragments of a few others have since been identified. None show any sign of horns. Picture stones and carvings from the period also show warriors in plain or pointed helmets.

Horned helmets did exist in Scandinavia, but much earlier. The famous Veksø helmets from Denmark date to the Bronze Age, around 900 BC, roughly seventeen centuries before the Vikings. They were likely ceremonial, not for battle. Later artists may have blended these much older finds with the Viking story, helping the myth seem plausible.

Horns make a costume instantly recognisable, which is exactly what stage designers, illustrators and later film makers wanted. A plain iron cap looks like any other medieval soldier.

Museums now often display the Gjermundbu helmet alongside explanations of the myth, using the popular image as a way into the real history.

Popular images of the past are often shaped less by evidence than by later art. Victorian painters gave Romans and Egyptians costumes that matched contemporary tastes, and Hollywood did the same. The horned Viking is one of the most durable examples, so familiar that sports teams, cartoons and costume shops all use it, even though historians have pointed out the problem for decades.

The real Vikings were farmers, traders and explorers as well as raiders. They sailed to North America, traded as far as Baghdad, and settled in places such as Iceland and Normandy.