The Celts, it is true, were only one of several races which from the east and north pressed westward and southward over Europe for a period of over a thousand years; but no invasion has ever been more complete or the effects of an invasion more profound and permanent. The Celts became identified with our island to a greater extent than either of their successors, the Saxons and Normans. The second body of them imparted to it its name. In the fifth century before Christ they had reached the Atlantic and had begun to invade Britain although the main body were near the Danube. In 387 B.C., they sacked Rome, and in the succeeding century a section of them crossed the Hellespont, overran Asia Minor and eventually settled in what became known as Galatia. The point of greatest importance at the present stage of our enquiry is that of the Celtic religion between the close of the Bronze Age and Cæsar’s invasion of Gaul and Britain. Was it one of the many forms of nature worship which found the central object of its adoration in the glorious orb who in the words of the Psalmist “cometh forth as a bridegroom out of his chamber and rejoiceth as a giant to run his course”? Did the worship of the sun form its most prominent distinguishing feature? The much-quoted passage given by Diodorus the Sicilian, who lived in the first century before the Christian era and who reproduced it from the _Description of the World_ written by Hecatæus in the fifth century, states that in the island of the Hyperboreans over against Celtica there is a magnificent circular temple which they have erected to Apollo.[17] The passage presents more than one difficulty. The Hyperboreans were known to the ancient world as the possessors of the sources of amber, a substance which is not found in Britain but in the neighbourhood of the Baltic. Those who would identify the Hyperborean island with Britain and the temple with Stonehenge, have to face the greater difficulty of accounting for the fact that a sepulchral structure erected in pre-Celtic times was, in the fifth century before Christ, being used for sun worship by Hyperboreans who may or may not have been Celts, but who in the passage are described as having erected it for that purpose. It should be remembered that Hecatæus had been dead for over a century when Pytheas the daring Greek explorer made his famous voyage of discovery, and that if that voyage was, as M. Déchelette contends,[18] to the navigator of the fourth century before the Christian era what a polar expedition is to the navigator of to-day, it is hardly likely that Hecatæus could have had very reliable information concerning either Britain or its Celtic inhabitants.