Syria's long-buried CW weapon of mass destruction

Ancient Background
The name Persia derived from a western Iranian tribe.  The Persian Empire, began in the 6th century BC.  At its greatest extent, it included modern Iran, Iraq, Syria, Jordan, Israel, Palestine, Lebanon, significant parts of ancient Egypt, Turkey, Black Sea coastal regions, Georgia, Afghanistan, northern Saudi Arabia, Pakistan, and more.

The Persian Empire's population by 480 BC was an estimated 50 million people (over 40% of the world's population at the time).

Dura-Europus, was a Roman border city built above the right bank of the Euphrates river in today's Syria.

Modern Archelogical  Finds
In January 2009, researchers found evidence that the Persian Empire used poisonous gases at Dura against Roman soldiers.  A University of Leicester archaeologist suggests asphalt and sulpur crystals were ignited to generate sulfur dioxide gas in defensive tunnels. 

In other words, Syrians circa 256 AD had copied the use of chemical warfare by Spartans during the Peloponnesian War (429 BC). 

Almost 2,000 years ago, 19 Roman soldiers rushed into a cramped underground tunnel, prepared to defend the Roman-held Syrian city of Dura-Europos from an army of Persians digging to undermine the city's mudbrick walls. But instead of Persian soldiers, the Romans met with a wall of noxious black smoke that turned to acid in their lungs. Their crystal-pommeled swords were no match for this weapon; the Romans choked and died in moments, many with their last pay of coins still slung in purses on their belts.  source

 More here.

Submarines areal ways silent and strange.