Julius Caesar (100-44 BC) mentioned that the place of possible origin of druidism was in Britain. Some have argued over the centuries in favour and against this statement. Caesar was only stating the possibility because he doesn’t know for fact of the druidic origin.
The Greek city in southern France, Massilia (modern Marseille), had traded with the Celts in the 6th century BC. The Romans have known the existence of Celts or the Gauls, as they called them, when several Gallic tribes had crossed over the Alps, settling in northern Italy, exerting pressure upon the Etruscan city-states during second half of the 5th century BC. The Roman had their own encounter with Gauls, when they were defeated at the Battle of Allia, in 391 BC. In the following year, the Gauls sacked Rome before leaving. The Romans had also fought the Gauls before (in the battle of Telamon, in Etruria, 225 BC) and during the Second Punic War against the Carthaginians, in third-quarter of the 3rd century BC. In none of these cases, was there any mention about the druids.
Some Celtic experts believed that this is proof that the druids didn’t exist among all Celtic people, such as those living in Gaul, Central Europe and in Galatea (in Asia Minor), so the druids must have come from Britain. There are even some who believed that the druids were not at all of Celtic origin. Some of the Celtic scholars believed that the druids were originally pre-Celtic people living in Brittany, Britain, and Ireland.
Arguing against that, it should be pointed out neither the Romans nor the Greeks had time to observe the customs of Gauls, and one could not possibly distinguish a druid when faced against the charge of fearless, sword-waving, head-hunting Gaulish warriors. There was probably existence of druids in Gaul 390 BC and even before this time, even though no one has seen one.
There are some who believed that the druids had lived in the time of the megalith period. One of the persistent, erroneous concepts about the druids is that they were the megalithic builders of burial mound or chamber, the standing stones and stone circle found throughout Europe, like the Stonehenge.
There are many large burial mounds can be found throughout central and western Europe. What is interesting is that there are spiral carving upon stones that are similar design to that we normally associate with Celtic work.
But these megalithic carvings are actually pre-Celtic, during the Neolithic period. These spiral carvings are often associated with the belief that it helps the passage of the soul to the Underworld. Yet, these megalithic carvings of spirals are not confined to British Isles and France. What can be found in Newgrange in Ireland or Gavrinis in France, can also be found in Spain, Sicily, and Malta.