How old are wooden barrels as a storage method?

[astro]

Making a sturdy, watertight wooden barrel out of staves and hoops is not all that simple. What is the first recorded instance in history of a barrel being used?

[Squink]

Barrels show up in the Bible, 1 Kings 18:33:

And he put the wood in order, and cut the bullock in pieces, and laid him on the wood, and said, Fill four barrels with water, and pour it on the burnt sacrifice, and on the wood.

However, God only knows what word it was that got translated into ‘barrel’.
This short History of Cooperage credits the Celts with inventing the modern barrel:

At around 350 B.C. the Celts elaborated rounded watertight recipients that were able to withstand stress (from rolling) and weight (from stacking). This is the barrel (tonneau) - from the Latin name “Dolium” meaning rounded. Ever since that time the barrel has been manufactured using basically the same techniques.

The photo of a “Gallo-Roman bas-relief showing a Gaulish boat carrying two wooden barrels” is pretty convincing, still, it is just a photo on a website.