Drinking-water wells are poisoned with rye ergot by Assyrians and Persians during the 6th and 5th centuries BC. During the same era, Assyrians catapult decaying animal carcasses over the walls of besieged cities.
During the Peloponnese War (431–404 BC) besieged cities are attacked with 'incendiary devices' and sulfur dioxides carried by the wind.
'Greek fire' (toxic smoke from an inflammatory mixture) is invented by Greek King Kallinikos. Greek fire remains the secret weapon of the Byzantine Empire against the Turks for five centuries. Later the Turks themselves use it to conquer the Greek Empire (14th century).
Roman Soldiers throw rotting animal corpses and poisons into their enemies' water supplies.
Barrels of blinding quicklime are catapulted by the English fleet on French vessels (middle of the 13th century).
A Tatar army tries to break the siege of Kissa in the Crimea by catapulting infected corpses over the city walls (14th century).
Bombs, grenades and rags containing arsenic are fired by the defenders of Belgrade against the Turks in 1456.
Weapons using sulfur, mercury, turpentine and nitrates are mentioned in military strategy books.
'Stinking Jars' and toxic bombs are used in great quantities during The Thirty Years' War (1618-1648).
More sophisticated devices using arsenic, orpiment, lead, ceruse, minium, verdigris, antimony as well as belladonna, euphorbe, hellebore, aconite and nux vomica are manufactured and perfected. We don't know if they were ever used.
British soldiers deliberately distribute smallpox-infected blankets as 'gifts' to Native American Indian tribes who have no immunity to the disease.
During the 19th century there was a shift away from the use of chemical weapons which, at this time, were not considered honorable.
English plans to fill the Russian garrison of Sevastopol with lethal smoke (using sulfur and coke) during the Crimean War (1854-1855) don't materialize.
Plans to use chlorine shells against the Confederates during the US War of Secession (1861-1865) are rejected.
6,000 cylinders containing 180 tons of chlorine are spread across 6km of the front near Ypres, Belgium. Driven by the wind, the cloud of gas kills 5 000 soldiers and puts a further 1500 out of action (April 22, 1915).
Attacks with a chlorinate-phosgene mixture at Bsura-Rumka on the Russian front. Over 12,000 bottles of the deadly gas are used, killing 6,000 and putting a further 3,000 out of action (May 31, 1915).
100,000 'T-shells' containing benzyl bromide are fired with cannons in Argonne, France (July, 1915).
Deadly phosgene shells are fired in Verdun, France (March, 1916).
Cyanhydric acid shells are used during the Battle of the Somme, France (July, 1916).
The first world war's reputation as a chemical war reaches its peak with the use of deadly mustard gas in the Ypres region of Belgium. Over 9,000 tons of the gas are produced and its use has a huge negative psychological impact on the soldiers (July, 1917).
The last year of the war sees massive use of shells containing aggressive gases by both sides. It is estimated that around 25% of the total shells used contained deadly chemicals.
The total loss of life caused by poisonous gases - especially mustard gas - during the first world war was 1,300,000 people. Of those, only 100,000 were on the battlefield. Were it not for the introduction and refinement of gas masks, the death toll would have been significantly greater.
While this amount of casualties is difficult to comprehend, it is worth noting that other 'conventional' weapons were responsible for a total 26,700,000 deaths during the same war. Of those, just 6,800,000 died on the battlefield.
1920: Chemical weapons are used during the Russian civil war.
1925: Mustard gas is used during the War of the Rif, Morocco. Significantly, this is the same year that the Geneva Protocol was agreed.
1935-36: Mustard gas is used in massive quantities against the warriors from Abyssinie, contributing to the destruction of Ethiopia.
1937 to 1941: Japan uses toxins against China, most notably during the attack of Yichang.
With the exception of the Far East, almost no chemical weapons were used by the warring parties during the second world war. There are two main reasons for this:
Unlike the static nature of the trench-warfare campaigns of the first world war, the second world war's 'Blitzkrieg' style of rapidly moving campaigns made the use of chemical weapon a less feasible option.
The allies were more advanced and had greater stocks of chemicals to use as weapons which acted as a deterrent to the Nazis.
During the 1950s, the United States and the forces of the NATO compete against the Soviet Union in the research and production of more sophisticated and effective chemical weapons.
Between 1963 and 1968, Egypt uses mustard gas in Yemen, while the United States uses defoliants, dioxin and weed-killers in Vietnam.
The Soviet war in Afghanistan (1979-83) sees the Soviet Union experiment with new, difficult-to-detect chemicals.
Between 1975 and 1983, Vietnam uses large quantities of toxins against the Laotian rebels.
During the Iran-Iraq War of the 1980s, Iraq uses mustard gas, cyanide and tabun against the Iranian troops resulting in very heavy losses (10,000 seriously wounded and an unknown number of deaths).
In 1995, Iraq admits to the United Nations that it had loaded anthrax spores into warheads during the Gulf War (1990). That conflict proved to be a major event in the history of chemical warfare by highlighting the threat that the Iraqi chemical arsenal posed to the international community. Their chemical arsenal was found to be the third biggest in the world containing some 50,000 mustard gas, sarin and sarin cyclohexylic shells and bombs.
It's worth noting that Iraq signed up to the Geneva Protocol in 1931.
Iraq uses tabun and mustard gas in massive quantities against the Kurds and Shiites in the south, causing thousands of deaths.
In 1984, the Bhagwan Shree Rajneesh cult allegedly contaminates salad bars in 10 restaurants in The Dalles, Oregon, with Salmonella Typhimurium, causing several hundred people to become ill.
Between 1987 and 1990, the United States, after 19 years of interruption, resumes the production of chemical weapons to catch up with the Soviet Union.
1969: Off the Belgian coast, one or two barrels of mustard gas leak into the sea killing seals and fish. Fishermen are burned as well as children on the beaches.
1979: A child is killed near Hamburg, Germany, by a stock of cartridges loaded with tabun.
1990: In the Libyan desert of Tarhunah (near Tripoli), the Rabta factory, thought to be the biggest of all chemical weapons factories, is destroyed in a mysterious fire.
1995: A terrorist attack using sarin in the Tokyo subway kills 8 and makes dozens of others seriously ill.