Use of Chemical Warfare Agents in Ancient History. A Case of Persians and Romans in Dura-Europos, Modern Syria in 256 C.E.

Background: Chemical warfare agents (CWA) were most notably used during the First World War in Europe, against Iranians and Kurdish citizens of Iraq at the hands of Saddam Hossein’s regime in 1980s and more recently in Syria. The use of CWA is banned under the international law. Methods: Ancient uses of CWA are not well studied. Recently, their use during the Persian siege of the Roman-held Dura-Europos (Salihiyah) in modern Syria in 256 C.E. has been theorized by revisiting the archaeological findings from Dura-Europos from the 1930s. Case study: The paper describes the history of Persia (Iran) and Rome in that era and particularly Shapur I, the second King (Shah) of the [Sasanian] Persian Empire (215 - 270 C.E.) and Valerian, Publius Licinius Valerianus Augustus, the Roman Emperor (193/200 - 264 C.E.). In addition, composition of the potentially applied CWA and clinical findings related to the exposure are postulated through a medical toxicology lens taking into account archeological evidence (carbonized top of the tunnels and bodies and yellow crystals found in the tunnel), recent research and contemporary historical notes.  Conclusion: It is plausible that a combination of fire accelerant or so called pitch (oil based substance, naphtha, bitumen or crude oil) and Sulphur dioxide (SO2) were used in this occasion. SO2 in combination with water on the body membranes creates highly toxic sulphurous acid (H2SO3) which is life threatening in a small enclosed space. As a result, a burning sensation in the nasopharynx and eyes, coughing, dyspnea, choking that led to pulmonary edema and death would have shortly followed. Severe clinical manifestations, panic and consequent mass hysteria of the toxic exposure should have prevented any organized retreat. In this incident, nineteen Roman and one Persian soldier were killed.