In approximately 256 C.E. Dura-Europas, a Roman fort known as “the Pompeii of the Syrian Desert,” fell victim to a Sasanian Persian siege in what is now Syria. When archeologist Simon James investigated the site several years ago, he found traces of yellow sulfur crystals and pitch near a pile of bodies—Roman soldiers who had died in the battle. This evidence points to a different kind of death for the 19 entombed Romans. As Discovery News reports, around 1,700 years ago, Syria was site to one of the first chemical gas attacks known in history.

In an American Journal of Archeology paper, James explains the implications:

Recent reanalysis of the excavation archive suggested that the mine evidence still held one unrecognized deadly secret: the Roman soldiers who perished there had not, as Robert du Mesnil du Buisson (the original excavator) believed, died by the sword or by fire but had been deliberately gassed by the Sasanian attackers.

With the federal government debating how to respond to sarin gas attacks in Syria, Discovery News looked into the history of chemical warfare in the area. Depending on how you define chemical weapon, however, Syria may not be the first site of such an attack, Discovery found. In a Greek siege in 590 B.C.E., enemies poisoned the water supply for the ancient city of Kirra with noxious hellebore (also known as Christmas roses). During the Peloponnesian War, the Spartans reportedly created toxic gas by burning sulfur. A burning ball of sulfur, pitch and barite was hurled in a 327 B.C.E. battle in Pakistan, too. And several years later, Harmatelians were hurling poison-tipped arrows at Alexander the Great’s army, also in Pakistan.

More from Smithsonian.com:

The Pentagon Just Built a Mobile Chemical Weapons-Neutralizing Facility

How Can the U.S. Government Know If Syrian Combatants Were Affected by Sarin Gas?