The "Black Death" was brought to Europe by Genoese merchants fleeing Tartar siege of their Caucasus cities. The Tartars catapulted the corpses of the dead, infected with Yersinia pestis, in order to kill the defenders with this biologic weapon. The rich and poor died alike in during the plague, as is testified by numerous documents and literary works, such as the Decameron, depicting the wealthy attempting to flee the plague without success. The sociopolitical infrastructure collapsed with 33% of the Europeans dead in all classes of society. Europe had to rebuild itself, with labor becoming a scarce resource; perhaps, this lack of manpower drove the Europeans to rely more on mechanical means of production, rather than using mass labor force like the Oriental empires.