(Not all alleged uses have been verified) 1710: Russians besieging Swedish troops at Reval throw bodies of plague victims over city walls. 17th-century `plague doctor' in protective clothing: coat of waxed cloth, gloves, glasses, and a `trunk'' with stuffing soaked in oils. 4th century BC: Spartans use mixtures of pitch and sulfur to wear down enemies with fumes during Peloponnesian War. 1763: British commander at Fort Pitt, in Ohio, sends two blankets and a scarf, ostensibly to mollify two Indian chiefs. The items had been used by smallpox victims; the result is an epidemic among the American Indians, who had no natural immunity. World War I: In April 1915, German troops open valves on first of 5,000 canisters of chlorine gas near Ypres, Belgium. By June 1916, Allies retaliate with phosgene and chlorine. In 1917, Germany introduces mustard gas, which can penetrate uniforms to cause painful burns. Nearly 125,000 tons of poison gases are used in WW1. Of the 1.3 million gas casualties, 91,000 (7%) die. Untold numbers are disabled for life. 1925: 29 nations sign Geneva Protocol, outlawing use of poison gases in war. (US Senate ratifies agreement 50 years later, in 1975.) 1935-36: Italy allegedly uses mustard gas against Ethiopian troops. 1939-44: Japanese Army uses chemical weapons against Chinese armies and civilians. Japan is also accused of biological warfare. 1951-53: Soviet Union, China, North Korea accuse US of using chemical weapons and practicing biological warfare in North Korea and China. 1957: East-bloc press accuses Britain of using biological weapons in Oman. Vietnam war: US admits using riot-control agents and herbicides (Agent Orange), but denies use of lethal agents or biological weapons. Herbicide use discontinued in 1967. 1963-67: Egypt charged with using chemical weapons, with Soviet help, during Yemen civil war. 1962-68: US charges Vietcong with using poison and biological weapons. Mid to late 1970s: Vietnam reportedly uses chemical weapons on Hmong resistance in Laos, and in Cambodia. 1972: More than 100 countries accede to Biological Weapons Convention, which bans development, production, and stockpiling. 1980: Ethiopian government forces suspected of using chemical weapons on Eritrean rebels. 1980-84: Afghan resistance and US charge Soviets with using chemical weapons, as well as experimental agents and biological toxins in Afghanistan. 1983-84: Iran raises issue of Iraqi chemical weapons use, later validated by UN team. March 1988: Iraq uses poison gas on Iranian-occupied Kurdish town of Halabja. Up to 5,000 civilians reportedly killed. August 1988: Thousands of Iraqi Kurds flee to Turkey, claiming Iraq used chemical agents against civilians.