Ammianus Marcellinus (325×330 CE – c.391) was a Roman historian born somewhere in the Greek-speaking states of the east. He was a soldier in the army of Constantius II and spent time in Gaul and fighting along side Gaulish soldiers in Roman units. His work has been noted as focused on military interests and exploits, sometimes to the detriment of his objectivity and other details.
The following is an adaptation of Ammianus Marcellinus, trans. John C. Rolfe. Cambridge: Harvard University Press, 1935-1940.
§ 15.9. I think now a suitable time to describe the regions and situation of the Gauls, for fear that amid fiery encounters and shifting fortunes of battle I may treat of matters unknown to some and seem to follow the example of slovenly sailors, who are forced amid surges and storms to mend their worn sails and rigging, which might have been put in order with less danger. The ancient writers, in doubt as to the earliest origin of the Gauls, have left an incomplete account of the matter, but later Timagenes, a true Greek in accuracy as well as language, collected out of various books these facts that had been long forgotten. Following his authority, and avoiding any obscurity, I shall state these clearly and plainly.
Some asserted that the people first seen in these regions were indigenous, called Celts from the name of a beloved king and Galatae (for so the Greek language terms the Gauls) from the name of his mother. Others stated that the Dorians, following the earlier Hercules, settled in the lands bordering on the Ocean. The druids say that a part of the people was in fact indigenous, but that others also poured in from the remote islands and the regions across the Rhine, driven from their homes by continual wars and by the inundation of the stormy sea. Some assert that after the destruction of Troy a few of those who fled from the Greeks and were scattered everywhere occupied those regions, which were then deserted.
But the inhabitants of those countries affirm this beyond all else, and I have also read it inscribed upon their monuments, that Hercules, the son of Amphytrion, hastened to destroy the cruel tyrants Geryon and Tauriscus, of whom one oppressed Spain, the other, Gaul. Having overcome them both he took to wife some high-born women and begat numerous children, who called by their own names the districts which they ruled. But in fact a people of Asia from Phocaea, to avoid the severity of [Harpagus], prefect of king Cyrus, set sail for Italy. A part of them founded Velia [now Castellamare della Bruca] in Lucania; the rest founded Massilia in the region of Vienne. In later eras they established many towns, as their strength and resources increased.
But I must not discuss varying opinions, which often causes satiety. Throughout these regions men gradually grew civilized and the study of the liberal arts flourished, initiated by the bards, the [vates] and the druids. The bards sang to the sweet strains of the lyre the valorous deeds of famous men composed in heroic verse, but the [vates], investigating the unknown, attempted to explain the secret laws of nature. The druids, being loftier than the rest in intellect, and bound together in fraternal organizations, as the authority of Pythagoras determined, were elevated by their investigation of obscure and profound subjects, and scorning all things human, pronounced the soul immortal. […]
§ 15.11. In early times, when these regions lay in darkness as savage, they are thought to have been threefold, divided into Celts (the same as the Gauls), the Aquitanians, and the Belgians, differing in language, customs, and laws. Now the Gauls (who are the Celts) are separated from the Aquitanians by the Garonne river, which rises in the hills of the Pyrenees, and after running past many towns disappears in the ocean. But the Gauls are separated from the Belgians by the Marne and the Seine, rivers of identical size; they flow through the district of Lyons, and after encircling in the manner of an island a stronghold of the Parisii called Lutetia, they unite in one channel, and flowing on together pour into the sea not far from Castra Constantia. Of all these nations the Belgae had the reputation in the ancient writers of being the most valiant, for the reason that being far removed from civilized life and not made effeminate by imported luxuries, they warred for a long time with the Germans across the Rhine. The Aquitanians, on the contrary, to whose coasts, as being near at hand and peaceable, imported goods are transported, had their characters weakened to effeminacy and easily came under the sway of Rome. […]
§ 15.12. Almost all the Gauls are of tall stature, fair and ruddy, terrible for the fierceness of their eyes, fond of quarreling, and of overbearing insolence. In fact, a whole band of foreigners will be unable to cope with one of them in a fight, if he call in his wife, stronger than he by far and with flashing eyes; least of all when she swells her neck and gnashes her teeth, and poising her huge white arms, proceeds to rain punches mingled with kicks, like shots discharged by the twisted cords of a catapult. The voices of most of them are formidable and threatening, whether they are good-natured or angry. But all of them with equal care keep clean and neat, and in those districts, particularly in Aquitania, no man or woman can be seen, regardless of how poor she might be, in soiled and ragged clothing, as elsewhere. All ages are most fit for military service, and the old man marches out on a campaign with a courage equal to that of the man in the prime of life; since his limbs are toughened by cold and constant toil, and he will make light of many formidable dangers. Nor does anyone of them, for dread of the service of Mars, cut off his thumb, as in Italy: there they call such men murci, or cowards. It is a race greedy for wine, devising numerous drinks similar to wine, and some among them of the lower social orders, with wits dulled by continual drunkenness (which Cato’s saying pronounced a voluntary kind of madness) rush about in aimless revels, so that those words seem true which Cicero spoke when defending Fonteius: “The Gauls henceforth will drink wine mixed with water, which they once thought poison.” […]