The oldest surviving references to the Celts are very brief and purely casual. Herodotus, writing in the mid-fifth century BC mentions them in connection with the whereabouts of the source of the Danube, and Hecataeus, who flourished somewhat earlier (c. 540-475 BC) but whose works is only known from later quotations, described the Greek colony of Massilia (Marseilles) as having been founded in the land of the Ligurians near the land of the Celts. Hecataeus elsewhere mentions a Celtic town called Nyrax, and this place seems best to be identified with Noreia in the ancient region of Styria in Austria. Herodotus is not primarily concerned with either the source of the Danube or with the Celts in his surviving work The Histories. This is a misfortune for his account of peoples of whom he has first hand knowledge, especially the Scythians, has been shown, with the aid of archaeology to be of great value. What does seem important is that both he and Hecataeus could already mention the Celts to the Greeks without any need of explanation. It seems safe then to deduce that, at the time of Herodotus, the Greeks recognized the Celts to be a major barbarian people living west and north of the Western Mediterranean and beyond the Alps. Ephorus, writing in the 4th century BC, counted the Celts among the four great barbarian peoples of the known world. The other three were the Scythians, Persians and Libyans. The geographer Eratosthenes, in the following century, showed them as widespread in Western and trans-Alpine Europe.

Following the Classical historians, we can make a brief summary of the intrusion of the Celts on the literate world of the Mediterranean.

About a quarter of a century after the death of Herodotus, Northern Italy was invaded by barbarians coming through the Alpine passes. These invaders were Celts as is shown by their names and description, but the Romans called them Galli from which Gallia Cis- and Trans-Alpina were derived. Polybius writing more than 2 centuries later refers to the invaders as Galatae and this word was widely used by Greek writers. On the other hand, it was recognized by Diodorus Siculus, Caesar, Strabo, and Pausanias, that Galli and Galatae were eqivalent names for Keltoi/Celtae, and Caesar makes it clear that the Galli of his time knew themselves by the name Celtae. Diodorus used these names indiscriminately but considered Keltoi the more correct word. Strabo says this word was known to the Greeks because of these people living behind Massilia. Pausanias, too, gives prior antiquity to Celts rather than to Galatians or Gauls. It would probably be impossible to unravel the true story of this ambiguity in names. It is safe to conclude however, that the Celts long continued to regard themselves by this name however many other names within their nation may have come to the fore from the 5th century BC.

The Galli or Gauls, as is the better known English version, settled in Italy first in the upper valley of the Po and its tributaries. They proceeded to first overrun the Etruscans. That they knew of the Etruscans and had traded with them over a long period of time is well demonstrated by the archaeological evidence.

The later Roman historians thought that these Celtic invaders had come from the northwest, from Gallia Transalpina as known from the 2nd century BC. The archaeological evidence is the invaders had come the way of the central Alpine passes and that their home had lain in Switzerland and Southern Germany. The names of the principal invading tribes are recorded. The Insubres are reported as the first arrivals and they eventually established their center at a place they called Mediolanum, the forerunner of Milan.

The Insubres were followed by at least four other tribes who settled in Lombardy. Later comers were the Boii and Lingones who had to pass through this region to find room in Emilia and the latest immigrants, the Senones, settled in less rich land along the Adriatic coast of Umbria. Not only did the Celtic invaders move as would be settlers with their families and possessions, but fast moving warrior bands raided far to the south. Apulia and even Sicily were reached and Rome was a prime target from its successful sacking about 390 BC to the decisive battle of Telamon in 225BC when a vast Gaulish army, including warriors freshly brought from beyond the Alps, was caught between two Roman forces and defeated. The end of Cisapline Gaulish independence came only in 192 BC when the Romans defeated the Boii at their stronghold....a place that was to become modern Bologna.