Interesting article about chemical warfare in Roman Syria was posted by the University of Leicester:
"A researcher has identified what he says may be the oldest archaeological evidence for chemical warfare: a poison-gas attack that killed about 20 Roman soldiers in the waning years of their Empire.Some additional info on the study of the Roman base:
The grim events occurred in a mine at the city of Dura-Europos, Syria, around 256 A.D., according to archaeologist Simon James of the University of Leicester, U.K.
The city, on the river Euphrates, had been conquered by the Romans, who installed a large garrison. The city later suffered a ferocious siege by an army from the powerful new Sasanian Persian empire. The dramatic story is known entirely from archaeological remains; no ancient text describes it, James said.
Excavations during the 1920s-30s, renewed in recent years, have resulted in spectacular and gruesome discoveries, he added.
The Sasanians used the full range of ancient siege techniques to breach the city. These included building “mines” or tunnels underneath the city walls in an attempt to make them collapse.
Roman defenders responded by building “counter-mines” to thwart the attackers, James said. In one of these narrow, low galleries, a pile of bodies—about 20 Roman soldiers still with their weapons—turned up in the 1930s. James recently revisited the site to understand how the warriors died.
“It is evident that, when mine and countermine met, the Romans lost the ensuing struggle,” he said. “Careful analysis of the disposition of the corpses shows they had been stacked at the mouth of the countermine by the Persians,” he added. The Persians had used their victims “to create a wall of bodies and shields, keeping Roman counterattack at bay while they set fire to the countermine, collapsing it.”
“This explains why the bodies were where they were found. But how did they die? For the Persians to kill 20 men in a space less than two meters high or wide, and about 11 meters long, required superhuman combat powers—or something more insidious.”
Finds from the Roman tunnel revealed that the Persians used and sulfur crystals and bitumen, a natural, flammable, tar-like substance, to get it burning, he added. These chemicals provided the vital clue, James said: when ignited, they give off dense clouds of choking gases.
The Persians evidently “heard the Romans tunnelling,” said James, “and prepared a nasty surprise for them.” When the Romans broke through, the Sasanians apparently set fire to the chemicals and pumped the gases in the Romans’ direction using bellows, he added.
“The Roman assault party were unconscious in seconds, dead in minutes. Use of such smoke generators in siege-mines is actually mentioned in classical texts, and it is clear from the archaeological evidence at Dura that the Sasanian Persians were as knowledgeable in siege warfare as the Romans; they surely knew of this grim tactic.”
Ironically, this Persian mine failed to destroy the walls, but the Sasanians somehow broke into the city anyway, James said. He has excavated a row of catapult bolts, ready to use by the wall of the Roman camp inside the city, representing the garrison’s last stand during final street fighting.
The defenders and inhabitants were slaughtered or deported to Persia, the city abandoned forever, leaving its gruesome secrets undisturbed until modern archaeological research began to reveal them. James presented his findings at the meeting of the Archaeological Institute of America in Philadelphia last week.
I found this bit about Dr. James paper on the subject as well:
"Death in the Dark, Blood in the Streets: New Insights into the Siege and Fall of Dura-Europos
Simon James, University of Leicester
Around A.D. 254, anticipating renewed invasion of Syria by the Sasanians, the Roman garrison of Dura-Europos massively strengthened the city’s defences, intending to hold it at all costs. The Sasanian attack came c. 256, in a ferocious siege known entirely through archaeology: no historical account survives. This involved the full range of known siege techniques, including artillery, an assault ramp, mines, and countermines. The mine complex around Tower 19 has provided especially gruesome testimony of underground combat, which the speaker argues included the earliest archaeological evidence for “gas warfare.” Other recent research has identified evidence for street fighting during the fall of the city to the Persians, and of the fate of the civil population. Permanent abandonment of the site meant these dramatic remains lay undisturbed until its rediscovery in 1920. Dura exemplifies the potential of archaeology for investigating ancient warfare. Continuing work by the speaker and others also illustrates the value of archival reexamination of early excavations, and of new, limited-scale, targeted fieldwork at “old” sites.
"Building on his recently-completed study of the spectacular finds of Roman and Sasanian military equipment from Dura, Simon James is now studying other aspects of the Roman military presence in the city. This includes some further work on the remains from the siege itself, and a primarily archaeological study of the Roman military base in the city. In contrast to the West where the imperial armies were normally housed in custom-built fortified bases, in the East urban basing of garrisons was routine. Dura provides the only archaeologically accessible, and reasonably well explored example of such an urban base from the principate." - More
And a nice image of a fresco discovered at Dura-Europos: