Mayor described the skirmish in the tunnel and the presence of burnt residue as an early example of archaeological evidence for a chemical incendiary in her 2003 book "Greek Fire, Poison, Arrows and Scorpion Bombs."
According to the scholar, a possible contender for the earliest archaeological evidence for a chemical weapon is a charred, manmade fire ball from the archaeological battle site at Gandhara, Pakistan.
"The burning missile had been hurled at Alexander's besieging army in 327 BC. Chemical analysis revealed the ball's composition included sulfur, barite, and pitch," Mayor said.
The ball was certainly ignited in a fire, but whether this was deliberate or accidental is impossible to establish.
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Long before World War I, when 39 different toxic agents - ranging from simple tear gas to mustard gas - were extensively used, it was a mixture of sulfur and pitch that gassed enemies.
Greek historian and Athenian general Thucydides described how, during the Peloponnesian War, the Spartans created a sulfur and pitch (in this case pine resin) fire at the siege of Plateia, Greece, in 429 BC.