Riddle of 'Baghdad's batteries'
It was in 1938, while working in Khujut Rabu, just outside Baghdad in modern day Iraq, that German archaeologist Wilhelm Konig unearthed a five-inch-long (13 cm) clay jar containing a copper cylinder that encased an iron rod. The vessel showed signs of corrosion, and early tests revealed that an acidic agent, such as vinegar or wine had been present. More than 60 years after their discovery, the batteries of Baghdad - as there are perhaps a dozen of them - are shrouded in myth. Most sources date the batteries to around 200 BC - in the Parthian era, circa 250 BC to AD 225. Skilled warriors, the Parthians were not noted for their scientific achievements.