The "Celts" are a somewhat problematic historical construction. As a somewhat linked culture, they existed all across northern and western Europe - Iberia, Gaul, Switzerland, Northern Italy, and Britain. Politically, however, they were never united in any way close to a "civilization." As currently constructed, they roughly represent Gaul, which was at least once roughly unified under Vercengitorix, though of course they can spread. I follow some of the Rome Total War mods still under creation, and most of the most historical of those tend to avoid "Celts" or "Gauls" as constructs, preferring instead individual tribes or smaller geographic confederacies. We have a choice with this mod, though. How should we use the "Celts?"