When the Bubonic plague ravaged Europe in the 12th century the Jews were accused of poisoning wells in order to spread the disease to the Christian population.
The first massacres directly related to the plague took place in April 1348 in Toulon, Provence where the Jewish quarter was sacked, and forty Jews were murdered in their homes; the next occurred in Barcelona. In 1349, massacres and persecution spread across Europe, including the Erfurt massacre, the Basel massacre, massacres in Aragon, and Flanders. 2,000 Jews were burnt alive on 14 February 1349 in the “Valentine’s Day” Strasbourg massacre, where the plague had not yet affected the city. While the ashes smouldered, Christian residents of Strasbourg sifted through and collected the valuable possessions of Jews not burnt by the fires. Many hundreds of Jewish communities were destroyed in this period. Within the 510 Jewish communities destroyed in this period, some members killed themselves to avoid the persecutions. In the spring of 1349 the Jewish community in Frankfurt am Main was annihilated. This was followed by the destruction of Jewish communities in Mainz and Cologne. The 3,000 strong Jewish population of Mainz initially defended themselves and managed to hold off the Christian attackers. But the Christians managed to overwhelm the Jewish ghetto in the end and killed all of its Jews.
Of course, Jews died of the plague at the same rate as Christians, but because Christian Europe was steeped in Jew-hatred, the Great Mortality was just another in a long line of convenient excuses to massacre Jews and then, of course, steal their property.