Titus Livius (Livy), The History of Rome, Book 5
Benjamin Oliver Foster, Ph.D., Ed.

35. Presently another band, consisting of Cenomani led by Etitovius, followed in the tracks [p. 121]of the earlier emigrants; and having, with the¹ approval of Bellovesus, crossed the Alps by the same pass, established themselves where the cities of Brixia and Verona are-now. [2] After these the Libui came and settled, and the Salluvii —taking up their abode hard by the ancient tribe of the Laevi Ligures, about the river Ticinus. Then, over the Poenine Pass, came the Boii and Lingones, who finding everything taken up between the Po and the Alps, crossed the Po on rafts, and drove out not only the Etruscans, but also the Umbrians from their lands; nevertheless, they kept on the further side of the Apennines. [3] Then the Senones, the latest to come, had their holdings from the river Utens all the way to the Aesis. This was the tribe, I find, which came to Clusium and from thence to Rome, but whether alone or assisted by all the peoples of Cisalpine Gaul, is uncertain.

[4] The men of Clusium, alarmed by this strange invasion, when they beheld the numbers and the unfamiliar figures of the men and their novel weapons, and heard that on many afield, this side the Po and beyond it, they had put to flight the levies of Etruria; though they had no rights of alliance or of friendship with the Romans, except that they had refused to defend their kinsmen the Veientes against the Roman People; did yet dispatch envoys to Rome to ask help of the senate. [5] As for the help, they were unsuccessful; but the three sons of Marcus Fabius Ambustus were sent as ambassadors to remonstrate with the Gauls, in the name of the senate and the Roman People, against their attack on those who had done them no wrong, and were the Roman People's allies and friends. [6] The Romans, [p. 123]they said, would be obliged to defend them, even² going to war, if circumstances should make it necessary; but it had seemed preferable that the war itself should, if possible, be avoided, and that they should make the acquaintance of the Gauls — a new race to them —in a friendly rather than in a hostile manner.