At this juncture, I do not know where the Celts initially came from but I do know that in approximately 200 plus years Before the Common Era, they reportedly crossed into Asia Minor  (again only approximate - about 20,000 people - having women and children in their number) and consisted of three tribes.  I actually know the names of these tribes, and, no, I can't pronounce the tribal names as Gaelic has changed considerably over the years.  They apparently made use of the Bosporus (for more info) and the Hellespont (for more info. Prior to their crossing, they seemed to have resided in the mid-Danube area, and as before stated due to the paucity of relics not much can be firmly established. Once the presence of the Celts was learned if by the warring Kings of that area (north) of Greece) their assistance was sought notably be one King Nicodemes who was having a difficult time with Antiochus. In return for their services they were granted a large section of territory which became know as Galatia. Not necessarily out of the generosity of Nicodemes' heart, but because as it lay southeast of Bithynia which acted as a buff against the Seleucid empire. We speak here of Western Asia Minor.  The Celts were busy as bees over the next decades making a reputation as marauders - with at least 12 cities on the Mediterranean Coast feeling their blades.