H. 10.—­Pliny’s picture has the interest of having been drawn almost at the final disappearance of Druidism from the Roman world.  For some reason it was supposed to be, like Christianity, peculiarly opposed to the genius of Roman civilization, and never came to be numbered amongst the religiones licitae of the Empire.  Augustus forbade the practice of it to Roman citizens,[61] Tiberius wholly suppressed it in Gaul,[62] and, in conquering Britain, Claudius crushed it with a hand of iron.  Few pictures in the early history of Britain are more familiar than the final extirpation of the last of the Druids, when their sacred island of Mona (Anglesey) was stormed by the Roman legionaries, and priests and priestesses perished en masse in the flames of their own altars.[63] Their desperate resistance was doubtless due to the fact that Rome was the declared and mortal enemy of their faith.  So baneful, indeed, did Druidism come to be considered, that to hold even with the least of its superstitions was treated at Rome as a capital offence.  Pliny tells us of a Roman knight, of Gallic birth, who was put to death by Claudius for no other reason than that of being in possession of a certain stone called by the Druids a “snake’s egg,” and supposed to bring good luck in law-suits.[64]

H. 11.—­This stone Pliny himself had seen, and describes it (in his chapter on the use of eggs) as being like a medium-sized apple, having a cartilaginous shell covered with small processes like the discs on the arms of an octopus.  This can scarcely have been, as most commentators suppose, the shell of an echinus (with which Pliny was well acquainted), even if fossil.  His description rather seems to point to some fossil covered with ostrea sigillina, such as are common in British green-sands.  He adds an account of the Druidical view of its production, how it is the solidified poison of a number of serpents who put their heads together to eject it, and how, even when set in gold, it will float, and that against a stream.  This “egg,” it will be seen, was from Gaul.  The British variant of the superstition was that the snakes thus formed a ring of poison matter, larger or smaller according to the number engaged, which solidified into a gem known as Glain naidr, “Adder’s glass."[65] The small rings of green or blue glass, too thick for wear, which are not uncommonly found in British burial-places, are supposed to represent this gem.  So also, possibly, are the much larger rings of roughly-baked clay which occur throughout the Roman period.  For superstitions die hard, and Gough assures us that even in 1789 such “adder-beads” or “snake-stones” were considered “lucky” in Wales and Cornwall, and were still ascribed to the same source as by the Druids of old.