In 1346 the Mongol Empire under the rule of Janibeg Khan besieged Kaffa. According to the First Doctor, many of the Mongol soldiers were killed by the bubonic plague. One of the Mongol commanders ordered that the bodies be catapulted over the wall into the city, which subsequently fell after the illness took hold.
Dodo Chaplet feared the idea was possibly influenced by a similar strategy employed against the Mongols at Kiev in the 13th century, and it came to be regarded as the first instance of biological warfare. Soon, Genoese merchants travelled across the Mediterranean, spreading the plague to ports in southern Europe. It moved on to Spain, France, Germany and Britain, and then to Scandinavia and Greenland. One third of the European population died as a result of the plague. (PROSE: Bunker Soldiers)