Pathogenic microbes, and toxins that they produce, have been developed as possible agents of warfare.[19] Crude forms of biological warfare have been practiced since antiquity.[20] In the 6th century BC, the Assyrians poisoned enemy wells with a fungus said to render the enemy delirious. In 1346, the bodies of Mongol warriors of the Golden Horde who had died of plague were thrown over the walls of the besieged Crimean city of Kaffa, possibly assisting the spread of the Black Death into Europe.[21][22][23][24] Advances in bacteriology in the 20th century increased the sophistication of possible bio-agents in war. Biological sabotage—in the form of anthrax and glanders—was undertaken on behalf of the Imperial German government during World War I, with indifferent results.[25] In World War II, Britain weaponised tularemia, anthrax, brucellosis, and botulism toxins, but never used them.[26] The USA similarly explored biological warfare agents,[27] developing anthrax spores, brucellosis, and botulism toxins for possible military use.[28] Japan developed biological warfare agents, with the use of experiments on human prisoners, and was about to use them when the war ended.[29][30][31][32][33]