In 2010, archaeologists exploring a fifth-century fortress on a Swedish island found a pair of skeleton feet peeking out from a doorway. The team thought it odd that the ancient people had left a body unburied to rot within their village’s stone walls, which housed some 200 people.

When they later dug up the rest of the skeleton, the team discovered signs that the person had been murdered. Beside him they found the brutalized remains of another. And in houses nearby and on the streets they uncovered more human bones that had been butchered with swords, axes and clubs.