M. D'Arbois and others, accepting Cæsar's dictum that "the system (of Druidism) is thought to have been devised in Britain, and brought thence into Gaul," maintain that the Druids were priests of the Goidels in Britain, who imposed themselves upon the Gaulish conquerors of the Goidels, and that Druidism then passed over into Gaul about 200 B.C.[1004] But it is hardly likely that, even if the Druids were accepted as priests by conquering Gauls in Britain, they should have affected the Gauls of Gaul who were outside the reflex influence of the conquered Goidels, and should have there obtained that power which they possessed. Goidels and Gauls were allied by race and language and religion, and it would be strange if they did not both possess a similar priesthood. Moreover, the Goidels had been a continental people, and Druidism was presumably flourishing among them then. Why did it not influence kindred Celtic tribes without Druids, _ex hypothesi_, at that time? Further, if we accept Professor Meyer's theory that no Goidel set foot in Britain until the second century A.D., the Gauls could not have received the Druidic priesthood from the Goidels. Cæsar merely says, "it is thought (_existimatur_) that Druidism came to Gaul from Britain."[1005] It was a pious opinion, perhaps his own, or one based on the fact that those who wished to perfect themselves in Druidic art went to Britain. This may have been because Britain had been less open to foreign influences than Gaul, and its Druids, unaffected by these, were thought to be more powerful than those of Gaul. Pliny, on the other hand, seems to think that Druidism passed over into Britain from Gaul.[1006]