In Romeo & Juliet, the doomed Mercutio curses the Montagues and the Capulets as he dies, victim of the long-running feud that will soon claim two more victims. The idea of "plague" was not a theoretical concept in Shakespeare's time. Most scholars believe R&J was written between 1591 and 1495. By the 14th century, Black Plague had reduced the population of western Europe by as much as 100 million. Less than a decade after the debut of Romeo & Juliet, in 1603, London was hit with a plague that killed 38,000. The Great Longon Plague of 1665-1666 was the last major outbreak of Plague in England, which is a good thing because it killed 100,000 people, or bout 15% of London's population. Wishing a plague on a family is a terrible, terrible curse.