The Gallic Swordsman, introduced with the Celts in Civilization III: Play the World, replaces the Swordsman. It has faster movement at a 3/2/2 attack/defense/movement ratio. It requires Iron in the Strategic Resource box to make. It costs more than a normal Swordsman by 20 shields, being worth 50.
Civilopedia Entry
While the bulk of a Celtic army would typically consist of poorly armored spearmen, it was the warrior nobles who wielded swords that were the most feared. These Gallic Swordsmen were wealthier than their peers, and could afford to equip themselves not only with their slashing and stabbing sword, but also with a helmet and shield. They often charged into battle bare-chested or completely naked, occasionally wearing vividly patterned pants or cloaks. Similar to the Viking Berserker, Gallic Swordsman began their battles by viciously taunting their enemies, followed by a mad rush against enemy lines. Celtic warriors were also known to serve as mercenaries to numerous armies of the classical period. The best-known instance of this is when Celtic mercenaries joined Hannibal in his invasion of Italy during the 2nd Punic War, contributing to victories against Rome.