The Vikings, or Norsemen, were Scandinavian warriors who raided and colonized parts of Europe between the 9th and 11th centuries. During this period, they invaded England several times. In the 1990s, researchers found the remains of two humans, along with a horse, a dog, and a pig, in a Viking cemetery in Derbyshire, England. Using a technique called radiocarbon dating, they determined that all five had died between the 8th and 10th centuries. Later, researchers found a written record stating that Vikings had been in the area in the year 873—which means the remains dated from that year. 

Researchers wanted to piece together the story of the horse, the dog, and the pig. They knew Vikings had stolen some horses from people in England. Did they steal these particular animals? 

Researchers found the answer by studying strontium. Strontium is an element found in soil and water. It finds its way into plants—and, eventually, into the bones of animals and humans that eat those plants. By analyzing the strontium in the bones of the Derbyshire animals, the researchers learned that the animals had spent most of their lives in Scandinavia. They must have traveled with the Vikings across the North Sea to England.

The researchers concluded that the animals were companions for two reasons. One, the Vikings traveled on longboats, which were fairly small. The Vikings wouldn’t have taken their animals with them on this weeks-long journey unless they didn’t want to be separated from them. And two, the Vikings were buried with the animals, which suggests a closeness.