One of the major technological inventions in antiquity, most probable derived from boat building technologies, was the discovery, that the wood can be bowed and bent if it is heated. In barrel, production bowed planks of arched wood were made into staves then assembled and encircled using bands of iron. We should not forget that the development of ironworking technologies produced tools necessary for the working of hardwood such as oak. Previously there were loosely slatted buckets, but this difficult art of putting together a complex barrel was introduced by the Celts who used them mostly for the transporting of their beers and wines.
The barrel was very convenient for transportation since they were as watertight as the ceramic amphorae but stronger, lighter and easy to roll without hurting their back.The Celts were avid traders and as a result, most of central and western Europe was flourishing with the exchange of ideas, skills and artwork. After the Roman expansion to the north, they adopted this technology, which in a few centuries replaced the amphorae. It was Julius Caesar that even mentioned their use as weapons when filled with burning material they were rolled down on roman legionaries. The production method and the design were so efficient that barrel making has changed very little over the two millennia and is now almost identical as in the period when it was discovered.