Weapons of the Barbarians is Episode 8 of Season 2. It aired on July September 7th, 2003. Here's the synopsis from TV.com:
The Roman Empire seemed destined to conquer the world. Their relentless march was tested time and again against the unorthodox weaponry of the Celtic and Germanic Barbarian hordes. Join Peter Woodward and his Conquest team as they explore the weapons and strategies employed by the Barbarians to stand and triumph against the Roman tide.
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