A primitive gas mask in the shape of a bird's beak. A common belief at the time was that the plague was spread by birds. It was thought that by dressing in a bird-like mask, the wearer could draw the plague away from the patient and onto the garment the plague doctor wore. The mask also included red glass eyepieces, which were thought to make the wearer impervious to evil. The beak of the mask was often filled with strongly aromatic herbs and spices to overpower the miasmas or 'bad air' which was also thought to carry the plague. At the very least, it may have served a dual purpose, also dulling the smell of unburied corpses, sputum, and ruptured bouboules in plague victims. | Manuel Velasco via Getty Images

The Plague Likely Arrived in Europe During the Stone Age

Nomads migrating into Europe during the Stone Age may have brought the plague, setting the stage for epidemics like the Black Death, which killed at least 25 million people.

Map of proposed Yersinia pestis circulation throughout Eurasia. A) Entrance of Y. pestis into Europe from Central Eurasia with the expansion of Yamnaya pastoralists around 4,800 years ago. B) Circulation of Y. pestis to Southern Siberia from Europe. Only complete genomes are shown. | Aida Andrades Valtueña. Andrades Valtueña et al. (2017). The Stone Age Plague and its Persistence in Eurasia. Current Biology.
The remains of a male from which samples were taken for the study. His grave included a dagger, flint arrow heads, a bracelet and a bone pin. | Stadtarchäologie Augsburg