While excavating a Viking cemetery near the Swedish town of Köping, archaeologists discovered a pair of sword hilts protruding curiously from the earth. After further investigation, they determined that the handles belonged to Viking swords that had been thrust into the earth above two burials and had remained upright for 1,200 years. “Viking Age graves containing swords are very rare,” says Anton Seiler, an archaeologist working with Sweden’s National Historical Museums. “Graves where swords were set in a vertical position are even rarer.”

Because it would have taken a great amount of force to hammer the weapons through the soil and large stones that covered the burials, researchers do not believe the blades were in this position by chance. “It was clearly a conscious action,” Seiler says, though he is not certain why the swords were arranged in this unusual way. Perhaps, he says, it was a gesture meant to aid the deceased warriors’ journey to Valhalla. It also may have been a way of commemorating the dead. Family members visiting the graves would have been able to touch the sword handles, thereby maintaining a close connection with the departed.

Analysis of hair from 22 mummies found in southern Peru has revealed the earliest known use of San Pedro cactus, a source of mescaline, and the psychoactive plants that make up the drug ayahuasca. The majority of the mummies were unearthed in Cahuachi, a religious center used by the Nazca people starting around 100 B.C. Coca plants and the Banisteriopsis caapi plant, better known as the liana vine, are among the substances detected in the mummies’ hair. The plants are not native to the region and were probably transported across the Andes Mountains. Researchers found that the drugs of choice changed over time. Ayahuasca and mescaline became less favored and coca consumption became more common after the Wari Empire conquered the Nazca around A.D. 750.

This shift may indicate changes in religious rituals surrounding human sacrifice. The find included four trophy heads, including one belonging to a child, who were sacrificial victims, but there is very little evidence of what role psychoactive substances played in the rituals. Bioarchaeologist Dagmara Socha of the University of Warsaw believes the antidepressant effects of the drugs may have been an important reason for their use. “In the case of the children that were sacrificed,” she says, “they were given Banisteriopsis caapi, probably because it was important for them to go happily to the gods.”

For several centuries, between 5,550 and 4,750 years ago, Iberian farmers pursued a curious pastime: On palm-sized, trapezoidal slates, they engraved designs portraying creatures with round eyes and triangle-patterned coats. “It’s a local phenomenon pertaining to the southernmost part of the Iberian Peninsula,” says biologist Juan J. Negro of the Spanish National Research Council. Nearly 4,000 of these plaques have been recovered from megalithic tombs, pits, and other Copper Age (ca. 4500–2500 B.C.) sites in Spain and Portugal since the nineteenth century, and many archaeologists have assumed the engravings played a role in rituals, perhaps by representing goddesses. Recently, Negro and his colleagues have questioned this long-standing view.

Negro, who studies the remains of birds recovered from archaeological sites, noticed avian traits in the designs. Instead of goddesses, he thinks the designs depict owls, and that they were carved by children. Artificial intelligence software designed to recognize images also identified one of the plaques as depicting an owl. The youngsters, suggests Negro, may have chosen to sketch a familiar creature that provided a community service by hunting rodents that infested cereal stores.