Celtic symbols were among the most common on Celtic warriors, namely for intimidation tactics in battle.
Celtic knots would make their appearance on the upper chest and arms as well.
Animals were hugely symbolic among the Celts, and could also be counted among the woad tattoos seen on warriors (protection, ferocity, courage).
Swirls, La Tene, trinities, circles. Presumably to reflect organic energy (nature, wind, time, motion).
Additionally, Celtic warriors would typically amass impressive scars won from past battles. These in conjunction with the deep indigo of intricate line-art tattooing, and frightening hair standing on end would undoubtedly be an intimidating sight for any of their foes.
I hope you have enjoyed this article on the history of Celtic tattoos. Be sure to check out the links at the end of this page for more info on Celt symbolism and tattoo meanings.