The Celts did have notoriously poor discipline and organization, due to the high factionalized nature of their culture as well as the fact that, to them, warfare was a couple-day-long affair of raiding and then going home rather than a protracted eight-month campaign. However they did have good weapons and armor, and some tribes were very good at weapon and armor making. The average Gallic chieftain and many of his retinue would be armed very similar to a Roman Legionaire, with chainmail, a helm, a big shield, possibly greaves, and of course a big sword. However, that was just the chieftains. The vast majority of any Celtic army may not have been shirtless and dirty, but they did have basic weaponry and little or no armor, whilst being expected to go up against trained, professional soldiers with full body armor, helm, shield, the works. The average Celt vs. the average Legionnaire, the Celt was at a huge disadvantage.