I think the earlier or founding Celts may have possessed a significant amount of Haplogroup I1b along with R1b, as thier homeland was more in west central Europe than west europe proper, in times further past an even more eastern origin may have come into play for the proto celtic homeland, initially involving perhaps very little R1b. By the time they are first noted by roman authorities, a western settlement of celtic peoples was already long established in Iberia and the British Isles, but we dont know if these areas were celticized by cultural or ethnic transference, I believe it was more cultural with only limited physical migration, leaving the indigenous populations largely unaltered "until anglo-saxon times". So in effect, as the Celtic world was pushed further to the west by Germanic and Roman powers, the peoples who were now the celts had only a marginal direct genetic relationship to the founders of the earlier celtic cultures who were to the east. So today R1b is the strongest marker for Celtic peoples, but just as the non northwesternmost celtic peoples of today speak french, spanish and english under thier contemporary nations, further east , an even older substratum of celtic heritage is present in modern day Czech republic, Austria, Hungary and Switzerland.
Perhaps prior to western settlement, the cultural boundries of the early celts largely coincided with the Hallstatt and proceding La tene cultures.
8th Century BC
3rd Century BC
