I bought a book about various world mythologies, and I was reading about knights that would represent kings to settle wars and disputed rather than losing hundreds of men, was this an actual thing? Or is this merely folktales that're larger myth than life?
Your question is tricky because "Celtic Society" can cover not only very different geographic locations but also eras spanning hundreds (if not, thousands...) of years. You use the term "knight", so does this mean the question you're posing is one focused in the medieval era? Warfare differed greatly from era to era, is why I ask. Also, are you asking about Celtic mythology or are you asking about historical warfare?