You do realize that the Celts did not build Stonehenge, much in the same way that the Aztecs did not build Teotihuacán. Like any new arrivals, they simply culturally appropriated it. Stonehenge was in fact built by British Aboriginals - black people with blue eyes (go figure). It was also moved from its original location in Wales several hundred years after it was built, so must have been pre-culturally appropriated before the Celts showed up. The moral of the story is that history is nothing but a collection of thieving migratory people "discovering" stuff that other folks built.