In the 14th and 15th centuries, little was known about how germs cause disease. Medical practitioners suspected, however, that the stench of rotting bodies could spread illness. So when combatants used corpses as ammunition, these bodies were no doubt intended as biological weapons. Historians know of at least three cases:
1340 - Attackers hurled dead horses and other animals by catapult at the castle of Thun L'Eveque in what is now northern France. The defenders reported that "the stink and the air were so abominable ... they could not long endure" and negotiated a truce.
1346 - As Tartars launched a siege upon Caffa, a port on the Black Sea, they suffered an outbreak of plague. Before retreating, they flung the infected bodies of their comrades over the walls of the city. Fleeing residents carried the disease to Italy, helping to spark the second major epidemic of "Black Death" in Europe.
1422 - At Karlstein in Bohemia, attacking forces launched the decaying cadavers of men killed in battle over the castle walls. They also stockpiled animal manure in the hope of spreading illness. Yet the defense held fast, and the siege was abandoned after five months.