It seems things come in threes. Yesterday the Daily Telegraph (London) printed an article on the above featuring the work of Dr Simon James of Leicester University who has:
“.. found the oldest evidence of chemical warfare yet after studying the bodies of 20 Roman soldiers' found underground in Syria 70 years ago.
Clues left at the scene revealed the Persians were lying in wait as the Romans dug a tunnel during a siege – then pumped in toxic gas – produced by sulphur crystals and bitumen – to kill all the Romans in minutes.“For a short article there’s a surprisingly detailed description of siege warfare techniques at Dura-Europos (Syria) in the third century AD. Recommended.
Update: it’s also been covered in The Independent.