The Gauls formed up around the walls.

Clusium asked help from Rome, with whom, notwithstanding the rivalry between the Etruscan and Roman nations, she had lately been on good terms.

The Romans promised first their good offices with the Gauls, afterwards material support; and thus were brought face to face those two peoples, fated to continue for four centuries a struggle which was to be ended only by the complete subjection of Gaul.
The details of that struggle belong specially to Roman history; they have been transmitted to us only by Roman historians; and the Romans it was who were left ultimately in possession of the battle-field, that is, of Italy.

It will suffice here to make known the general march of events and the most characteristic incidents.
Four distinct periods may be recognized in this history; and each marks a different phase in the course of events, and, so to speak, an act of the drama.

During the first period, which lasted forty-two years, from 391 to 349 B.C., the Gauls carried on a war of aggression and conquest against Rome.