An ancient cemetery on the eastern shore of the Baltic Sea contains some surprising bodies. Here, 1100 years ago, prominent warriors were cremated and buried with grave goods including amber beads, axes, and silver jewelry. Also present: the skeletons of young horses. Travelers’ tales and archaeological clues suggest a cruel ritual, in which the animals were raced to exhaustion, then led into a pit and forced onto their knees before being buried alive.

Over the past 150 years, archaeologists have found thousands of horse burials in Latvia, Lithuania, Russia, and Poland dated between 0 C.E. to the 1200s. The bones reveal that the animals were usually killed at the prime age of between 3 and 5 years old. Some were buried whole; others were dismembered. Some were killed standing upright in pits; others were pinned on their sides under heavy stones and buried alive. In Viking Age Lithuania, the exhausted animals were forced to kneel on subterranean ramps and buried faced down as though galloping into the earth.