Actually, all things considered, I think that is actually an accomplishment. I mean, the Egyptians and Arabs even plundered the Pyramids of Giza for stone, so not plundering masonry as tempting as Stonehenge and Newgrange may be considered an accomplishment. What's even more amazing is that they somehow survived the English.You mean the achievement of Celts is what they didn't destroy what was built before them? Celts themselves appeared in about 800BC and arrived to British Islands later.