Chemical warfare has a long history, probably starting with the first stone-age warrior who smeared the juice of poisonous berries on his spearhead.

One of the earliest recorded examples of chemical warfare dates to about 429 B.C., during the Peloponnesian War. Thebes was besieging the city Plataea and unable to penetrate the town's defenses.

As Thucydides reported in "History of the Peloponnesian War" (translated by Richard Crawley in 1910), the Thebans "determined to try to effects of fire and see whether they could not, with the help of a wind, burn the town. . . . (they) lighted the wood by setting fire to it with sulphur and pitch.

"The consequence was a fire greater than anyone had ever yet seen produced by human agency. . . . A great part of the town became entirely inaccessible, and had a wind blown upon it, in accordance with the hopes of the enemy, nothing could have saved them."

But a thunderstorm intervened, putting out the choking fumes.

Sulfur also was a component to the chemical weapon known to the Eastern Roman empire as "Greek Fire." A mixture that also included naphtha and quicklime, the Byzantines shot it from bronze tubes mounted on their warships. They destroyed two Arab fleets with it in 678 and 717-18.

During World War I, 1914-18, both sides used poison gas, notably chlorine. One estimate is that 100,000 were killed and 900,000 injured by the blinding, choking fumes. Often soldiers were killed immediately by the drifting clouds of green-gray gas, but many died of pneumonia weeks after they were attacked because their lungs were damaged.

The combatants also used mustard agent, which burns skin and and lung tissue, and breaks the body's white blood cells and lymph tissues.

Italians gassed barefoot Ethiopian soldiers in the 1930s. Gas was used in the Iraq-Iran War. In 1987-88, Saddam Hussein's troops reportedly used poison gas on Kurds in Iraq.

When World War II began, President Franklin Roosevelt announced this country would not be the first to use poison gas, but would respond in kind if American troops were attacked. In a war that featured saturation bombing, incendiary bombing, terror rocket attacks and the atomic bomb, poison gas was not used.

Although neither side actually fired chemical weapons in World War II, Germans killed tens of thousands of concentration camp victims with Zyklon-B. Reportedly, Japanese also killed 3,000 prisoners of war in Zyklon-B experiments.

In one of the strangest tragedies of World War II, scores of Americans were killed by this country's own chemical weapons.