Historians used to say that the Druids couldnt have built Stonehenge and all the other stone circles in Britain, because the Druids were the priests of the Celts, and the Celts only arrived in Britain in 500 BCE. Since no stone monuments were built after 1400 BCE, they say a gap of half a millennium separates the last of the stone circles from the arrival of the Druids. But in the sixties many historians changed their minds. They realized that the origin of the so-called Celtic tribes was far more complex than originally presumed, and suggested instead that early or Proto-Celts were probably in Britain as early as 2000 BCE - when the great stone monuments were still being built - and that they were almost certainly involved in their design and construction.
Before the 1960s historians had thought there were Celtic tribes originating in central Europe, who had invaded Britain in 500 BCE. Since then, they have realized that a more accurate picture is one of the gradual development of a variety of local and incoming tribes, who slowly evolved common Celtic languages, and copied artwork from continental Europe. Rather than specific invasions, we have to imagine a constant and gradual shifting and inter-marrying of populations who spoke these languages and liked this style of art.
This view of a gradual development of Celticism restores Stonehenge to the Druids. Archaeologists and prehistorians had associated Druids with the construction and use of Stonehenge until the first half of the twentieth century, when improved dating for monuments seemed to make the connection impossible. If stone circles were no longer built in Britain after 1400 BCE and the Celts did not arrive until 500 BCE, the Druids could apparently not have been contemporary with megalithic monuments. Now academic opinion is divided. Some experts emphasise the lack of continuity between religious structures and practices in the second and first millennia BCE. Others, however, point to the new sense of continuity in the genetics and culture of the British, with the rejection of the idea of a Celtic invasion. This second school of thought makes it possible again to see the Druids as the priests and priestesses of the stone circles, a tendency reinforced by the increasing recognition of the importance of ritual astronomy in the construction of these monuments. As John Michell put it in A Little History of Astro-Archaeology : suddenly science restored the Druids to their old temple, Stonehenge, wiser and more venerable than before.