If the Syrian government is using chemical weapons, as opposition and aid groups maintain, the tactic would be horrific — but not new. One of the first known uses was during the Peloponnesian War (431-404 B.C.), when Spartans used arsenic smoke. A thousand years later, the Greeks spread gases during the siege of Constantinople (A.D. 637). Unionists proposed using chemical agents during America's Civil War (1861-65) but rejected the idea. Then during World War I, the first modern use of chemical warfare, more than 125,000 tons of toxins were dispersed, killing more than 100,000 people and injuring many more.