Livy (v. 34) describes how a horde…

Livy (v. 34) describes how a horde of Gauls led by Bellovesus crossed the Alps around 600 BCE (Tarquinius Priscus was reigning in Rome) and occupied the territory between Milan and Cremona, identifying the local inhabitants of his own time, the Insubres, with these invading Gauls.

The Celtic presence in Italy is dated to at least the seventh century BCE if not before, however, Italian and French archeologists and scholars, based on archaeological sources, in particular compared with Livy's passage documenting the arrival of Bellovesus and his Insubres at the time of the reign of Tarquinius Priscus (sixth century BCE), along with the founding of Mediolanum, modern Milan, around 600 BCE in an area yet "inhabited by Insubres".

Scylax of Caryanda, a Greek traveler and geographer active between 522 and 485 BCE, mentions the presence of Celtic-speaking peoples settled in northeast Italy in his Periplus of Scylax.

The text, rewritten about a century later after the loss of the original by a pseudo-Scylax, tells of a journey along the shores of the Mediterranean made by a Greek traveler who describes the Celtic tribes on the coast just south of the settlements of the Veneti.

The date should be about 490 BCE, given the known dates in the life of Scylax.