Filling a mass grave at night during the Plague of London, c 1665. [Getty Images]

UNITED KINGDOM - NOVEMBER 30: Engraving, possibly 19th century, showing a group of men with torches in a churchyard, preparing to empty the contents of a covered cart into the �Great Pit� in Aldgate. The bubonic plague is a disease caused by Yersinia pestis, an infection carried by fleas living as parasites on rats. The plague hit London in late 1664, having ravaged Holland the previous year, and killed around 100,000 people in and around the city. The dead were collected at night and thrown into common burial graves. Regular outbreaks of bubonic plague occurred in Britain and Europe in Medieval times and continued until the 17th century. (Photo by SSPL/Getty Images)

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