If Syrian President Bashar al-Assad has really carried out a chemical attack, it wouldn’t be the first time poisonous gas brought death in the Middle East country. 
 
 Indeed, right in Syria archaeologists have found some of the oldest evidence of chemical warfare. 
 
 According to University of Leicester archaeologist Simon James, who published his findings back in 2009, poison gas was used in Syria more than 1,700 years ago when a Roman fort at Dura-Europos became the site of a violent siege by the powerful Sasanian Persian empire. 
 
 BLOG: Why a Chemical Threat in Syria Is Terrifying 
 
 No historical record exists of the battle, which occurred around 256 A.D., but archaeological remains, unearthed by major excavations in 1920-1937 by teams from France and Yale University, and after 1986 by French-Syrian teams, helped James piece together the action. 
 
 Trying to enter the city, the Sasanians dug tunnels underneath its walls. Intending to hold their ground at all costs, Roman defenders responded with counter-mines. 
 
 In the 1930s, archaeologists unearthed dramatic evidence of the fight. In one of the tunnels, a pile of bodies, still completely fitted with their weapons and armour, testified to the horrors of the battle. 
 
 At the time, the researchers believed the trapped Roman soldiers had died after the tunnel collapsed. But according to James, residue of pitch (a resinous substance) and yellow sulfur crystals found in a jar lying near the bodies indicated a much more gruesome reality. 
 
 Indeed, the Sasanians placed fire pits strategically throughout the tunnel, and when the Romans broke through, they gassed them by adding sulfur crystals and bitumen to the fire. 
 
 BLOG: Why Chemical Weapons Cross the ‘Red Line’ 
 
 “Defining what constitutes a chemical weapon in antiquity is complex, but this is certainly one of the earliest archaeological finds of the addition of chemical accelerants to a fire to produce toxic fumes,” Adrienne Mayor, a research scholar in classics and history of science at Stanford University, told Discovery News. 
 
 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. 
 
 NEWS: What Are the Rules of War? 
 
 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. 
 
 The Boeotians, Sparta’s allies, used a similar chemical flame-thrower in 424 BC at Delium, combining burning coal, sulfur and pitch. 
 
 Aeneas Tacticus (360 B.C.), one of the earliest Greek writers on the art of war, suggested combining pitch and sulfur to defend against sieges. 
 
 “These are the earliest recorded uses of a chemically enhanced incendiary to create a poison gas,” Mayor said. 
 
 “The combustion of sulfur creates toxic sulfur dioxide gas. The fumes are lethal if inhaled in large quantities,” she added. 
 
 Image: At the Palmyrene Gate, the principal entrance to the city of Dura Europos, toxic gas brought death more than 1,700 years ago. Credit: Heretiq/Wikimedia Commons. ||||| Two millennia ago, a small Greco-Roman temple in present-day Turkey awed and enthralled its residents. Just beyond its stone gate, in a grotto shrouded in a heavy mist, a strange force worked dark deeds: Bulls ushered inside would lie down and perish; the castrated priests in charge would emerge unscathed. 
 
 Was it the bloodthirsty will of Pluto, the god of the underworld? The supernatural power of the priests? New research published on Feb. 12 in the journal Archaeological and Anthropological Sciences suggests a far earthlier explanation to the cave’s mystery: noxious carbon dioxide. 
 
 Using a portable gas analyzer, volcano biologist Hardy Pfanz led a team of scientists to discover that vapors emitted from the mouth of the cave—belched from a fissure running deep beneath the area—reached levels of 4 percent to 53 percent volcanic carbon dioxide, depending on the distance from the ground. The lower to the cave floor, the higher the amount of suffocating gas, which formed a lethal lake of carbon dioxide. (The noxious gas is heavier than oxygen, so it settles lower, which is one reason CO₂ leaks in your house make basements deadly.) Animals with noses to the ground likely breathed in far more gas than the humans walking upright beside them, which could explain the priests’ miraculous imperviousness. 
 
 View of the ruins of the city of Hierapolis, near modern-day Pamukkale, Turkey. Photographer: alla_iatsun/iStockphoto 
 
 Although rediscovered only in 2013 near the town of Pamukkale—famous for its surreal, Unesco-designate travertine hot spring terraces—the cave’s existence has been known since antiquity as part of what was then Hierapolis. Known as “Plutonium” after Pluto, it was thought to be a gate to the underworld and a way to convene with the god by offering animal sacrifices. Spectators would watch in disbelief from a nearby arena. A description written by the Greek geographer Strabo, who lived from 63 B.C. to 24 A.D., makes a great deal more sense given what we know today: “This space is full of a vapor so misty and dense that one can scarcely see the ground … bulls that are led into it fall and are dragged out dead,” he wrote. But although priests entered and left the cave unharmed, Strabo noted that they would “hold their breath as much as they [could]” and displayed “an indication of a kind of suffocating attack.” 
 
 The terraces of Pamukkale. Photographer: gloriasalgado/Room RF 
 
 Two thousand years later, visitors should still be wary of the gate; during the 2013 excavation, archeologists witnessed several birds drop dead after flying too close. 
 
 Granted, merely getting here might prove a challenge. Beginning in 2015, Turkey’s rough relationship with Russia has tanked its tourism industry, which despite a brief resurgence last year continues to suffer following tensions with the U.S. government. In December, the U.S. and Turkey mutually suspended visa services amid a feud over the arrest of a local employee of the U.S. Consulate in Istanbul. Services later resumed, but the U.S. government urged its citizens in January to hold off on travel plans to the region, citing terrorism concerns. 
 
 The silver lining? Fear generally keeps tourist crowds at bay. Should you visit, you might have the plutonium all to yourself.
– Amid all the uproar over chemical weapons in Syria comes this surprising revelation: What could be the earliest archaeological evidence of chemical weapons was uncovered in the country—and it is some 1,700 years old. A mixture of sulfur and pitch combined with fire was the first way humans gassed their enemies, explains Discovery News. It dredges up 2009 findings by British archaeologist Simon James, who asserts that such a poison gas was used during a siege on the Roman-controlled city of Dura-Europos around AD 256. The site was excavated throughout the 20th century, first in 1920; in the next decade, the bodies of 20 armor-clad Roman soldiers were found in one of the counter-mines they dug in order to access the tunnels made by the invading Sasanian Persians. The original theory was that the collapse of the tunnel killed them. But James offered proof that the Romans were actually gassed: A jar near the bodies contained residue composed of pitch and yellow sulfur crystals. National Geographic shares James' explanation: "I think the Sasanians placed braziers and bellows in their gallery, and when the Romans broke through, added the chemicals and pumped choking clouds into the Roman tunnel." Death would have come within minutes. There is one bit of archaeology that could predate it: a sulfur and pitch fireball that struck Alexander’s army in 327 BC. But a Stanford research scholar notes that there's no way to determine whether it was purposefully or accidentally ignited. (More on this history front: Researchers now say ancient Egypt sprang up faster than we thought.)