Almost 2,000 years ago, 19 Roman soldiers rushed into a cramped underground tunnel, prepared to defend the Roman-held Syrian city of Dura-Europos from an army of Persians digging to undermine the city's mudbrick walls. But instead of Persian soldiers, the Romans met with a wall of noxious black smoke that turned to acid in their lungs. Their crystal-pommeled swords were no match for this weapon; the Romans choked and died in moments, many with their last pay of coins still slung in purses on their belts.

These 20 men, who died in A.D. 256, may be the first victims of chemical warfare to leave any archeological evidence of their passing, according to a new investigation. The case is a cold one, with little physical evidence left behind beyond drawings and archaeological excavation notes from the 1930s. But a new analysis of those materials by Simon James, an archaeologist and historian from the University of Leicester in England, published in January in the American Journal of Archaeology finds that the soldiers likely did not die by the sword as the original excavator believed. Instead, they were gassed.
 

In the new interpretation of the clash in the tunnels of Dura, the Romans heard the Persians working beneath the ground and steered their tunnel to intercept their enemies. The Roman tunnel was shallower than the Persian one, so the Romans planned to break in on the Persians from above. But there was no element of surprise for either side: The Persians could also hear the Romans coming.

So the Persians set a trap. Just as the Romans broke through, James said, they lit a fire in their own tunnel. Perhaps they had a bellows to direct the smoke, or perhaps they relied on the natural chimney effect of the shaft between the two tunnels. Either way, they threw sulfur and bitumen on the flames. One of the Persian soldiers was overcome and died, a victim of his own side's weapon. The Romans met with the choking gas, which turned to sulfuric acid in their lungs.

"It would have almost been literally the fumes of hell coming out of the Roman tunnel," James said.

Source: Live Science via Αρχαιολογ?α Online, 09/03/11