For 10 points, name this disease that killed millions of fourteenth century Europeans.
This event caused members of a certain profession to begin wearing beak-like masks. Because of this event, a force of Tartars broke off their siege of Kaffa. Flagellants rose to prominence during this event, from which the nursery rhyme "Ring around the rosy" originated. This event was caused by yersinia pestis born by flea-bearing (*) rats. As a result of this event, the population of Europe fell by a third between 1348 and 1350. For 10 points, name this disease that killed millions of fourteenth century Europeans.
This event caused members of a certain profession to begin wearing beak-like masks.
{Black} Plague [or {Bubonic} Plague]