Horses were an important component of Baltic culture between the 1st and 13th centuries. Texts written by foreign travelers explain how elites drank fermented mare’s milk, and archaeologists have discovered numerous ancient equestrian artifacts.

The Baltic pagans did not know how to read or write before their conversion to Christianity, so many of their customs are not known today. About 1,000 years ago, however, these people decided to import horses to subject them to gruesome public sacrifices, according to an article published in the journal Science Advances.

Researchers have performed biomolecular analysis of 80 sacrificed horses, both male and female, found in ancient cemeteries in Russia, Poland and Lithuania showing that they were brought from Scandinavia using extensive trade networks that connected the Viking world to the Byzantine and Arab empires.

Equine rituals were highly visible and symbolic public events throughout prehistoric pagan Europe, and persisted among the Baltic tribes until the 14th century. Several horses were offered, a single complete animal or partial specimens. In many cemeteries in the area they were buried separately from humans, but there are numerous examples of animals with superimposed human cremations.

Until now it was believed that stallions were specifically selected as an offering and that this ritual – which often involved beheading, skinning, dismembering horses or burying them alive – was performed at the funerals of elite male warriors.

To test this hypothesis, the Cardiff University team analyzed the DNA of the horses and found that approximately 66% were stallions and 34% were mares. “Our results suggest that they did not exclusively select males,” they write in their study.

Horses were common in the Baltic territory, so experts had not questioned whether the animals were local or came from somewhere else nearby. But this work carried out an analysis of strontium isotopes of the horses’ tooth enamel to identify their origin and found that three were not born in the area.

The strontium present in the crowns of teeth comes from the early diet of animals. By measuring the ratio of two variants of the dentition or teeth that grew at different times, researchers can relate where the horse grew or see where it moved.

“The results confirm that there is no possibility that horses originated in the territory of the Baltic tribes and that the most likely region for these horses is the Fennoscandian peninsula, specifically east-central Sweden or southern Finland,” the researchers write.

The three horses were dated to between the 11th and 13th centuries, a time when trade networks across the Baltic Sea, particularly with Sweden, were well established. It was also a period when there was still pagan resistance within the Swedish kingdom, which officially converted to Christianity in 1164.

The fact that a horse not local to Kaliningrad was buried with a Scandinavian-influenced artifact (a weight, possibly involved in trade) may suggest that its Baltic owner was a pagan merchant, the archaeologists add. Although it is also possible, they point out, that the imported horses arrived with their Scandinavian owners and that they were buried in the Baltic style.

“In any case – they indicate – our results prove that horses raised by Christians crossed up to 1,500 kilometers across the Baltic Sea in cargo ships from the late Viking Age, a level of mobility not previously recognized.”