Simon James, an archaeologist at the University of Leicester, says that the Persian Empire used poisonous gases, produced by igniting bitumen and sulphur crystals, during the siege of the Roman city of Dura, Eastern Syria, in the 3rd Century AD.
The Persians dug a mine under the walls, and the Romans dug a counter-mine to intercept them — all standard operating procedure in an ancient siege.
The Persians then ignited the bitumen and sulphur crystals and likely used underground bellows or chimneys to rapidly overwhelm the Roman troops with deadly fumes:
“For the Persians to kill 20 men in a space less than 2m high or wide, and about 11m long, required superhuman combat powers — or something more insidious,” said Dr James.“The Roman assault party was unconscious in seconds, dead in minutes.”
Excavations showed that the soldiers’ bodies were stacked near the counter-mine entrance by the attackers to create a protective barricade before setting the tunnel on fire.
The Persian mine failed to collapse the city wall and adjacent tower, but the attackers nonetheless conquered the city.