Thus far the history, and from what we have said it will appear that the Celts first emerge in literature in the fifth century B.C., from which time the classical writers make frequent, though generally short and meagre allusions to them. Dr. W. Z. Ripley,[8] one of the latest authorities on ethnology, would discount their evidence as of little value for the purposes of modern scientific research into race origins and affinities, yet, nevertheless, so far as it goes, it is highly interesting and important. The earliest of all the Greek authors to mention the Celts, if we except the geographer Hecatæus (520 B.C.), is Herodotus (484–425?), who twice refers to them in his history as dwelling at the sources of the Danube and bordering on the Kunesii, the westermost inhabitants of Europe. Xenophon, at a later period (390), speaking of them as mercenaries with Dionysius of Syracuse in 368 B.C., remarks that “the ships brought Keltoi and Iberes.” Plato, Ephorus, Pytheas, and Scylax all furnish hints in the same century. Aristotle also knew about this extraordinary people, who, he was told, feared “neither earthquake nor floods,” living in a country so cold that even the ass did not thrive there, yet putting little clothing on their children. It appears he had also heard that they had sacked Rome. Timæus popularised the new name Galatæ in bringing into notice Galatia, which, he avers, is named after “Galates, son of Cyclops and Galatia.” From this time onward we get fuller details of the Celtic character, manners, and customs. And to show the number and variety of authorities from which information may be gleaned, the following may be selected: Polybius, a Greek writer of the second century B.C., and Posidonius of the first. Julius Cæsar and his contemporary Diodorus Siculus, Strabo, a geographer of the early part of the first century A.D., Virgil, Cicero, Livy, Tacitus, Dion Cassius, Pliny, Ptolemy, and Ammianus Marcellinus, the latter bringing the list down towards the end of the fourth century, when the Roman Empire in its own turn began to break up, and the Gaels were at length prepared to enter the arena of literature and speak for themselves.