It was the third century BC, namely the 222, when at the Clastidium (Casteggio in the Oltrepò Pavese, nda) the army of Rome, led by the Consul Marco Claudio Marcello, definitively closed the game with the Insubrish Gauls and the Geti, bringing to completion the conquest of the Italian peninsula; many small villages of huts that dotted the hills near the Tiber in just over five hundred years placed their political and military control over a territory of more than 100.000 km2, Rome became for the first time in history a formal reference point for the whole peninsula, inaugurating, perhaps unknowingly, its two-thousand-year history of capital.
The legions that defeated Viridomaro, king of the Gesati and leader of the Gallic tribes with capital Maediolanum allowed the Romans to reach the upper Po valley, in fact annexing the wide plain between today's historical regions of Emilia and Lombardy.
The Roman army of this very distant historical era was structured according to the manipulate model handed down to us in detail by Polybius: the legionaries were recruited annually on the Capitol between all the cives subject to military service obligations, in particular every citizen among the 18 and the 46 years, with an income not inferior to the 400 drachmas, was obliged to carry out from a minimum of 10 annual military campaigns, for the conscripts in cavalry, to a maximum of 16 military campaigns per year, for individuals framed in the infantry. The recruitment took place through a complex procedure that combined elections and selection from the youngest to the oldest to reach, at the end of the complicated formal mechanism, to have the Legion as a tactical unit constituted, based on census and census rules, in four groups named velites, hastati, princeps e triarii, with a total of 4200 men to which 10 squads of knights were added (turmae) for a total of 300 mounted units. This maneuvering force was increasingly accompanied by auxilia numerically equivalent, but with tasks complementary to those of the Roman legion and never as a reinforcement or reinforcement.
Returning to Clastidium, the Roman legionary mass, when the times were ripe, led by the consul Marco Claudio Marcello moved towards the fortified city of Acerrae, in the area currently between Cremona and Lodi, casus belli it was the dangerous offensive carried out three years before by the Galli Insubri near Talamone, an event that needed to be avenged in the name of the integrity of aUrbe which became ever wider according to the principle according to which the integrity of its central core, located on the banks of the Tiber, had to be safeguarded through expansionary actions.
In order to ease the pressure on Acerrae the insubrious, supported by Geti mercenary forces from the Rhone, aimed at Clastidium, city in the hands of the Marici, Ligurian population allied with the Romans. Having come to know the diversionary action devised by the roosters and their own allies, the Romans did not fall into the trap and sent cavalry units against the Celts which, through rapid winding actions, pushed their enemies towards a stream, probably the Cup, where many of these they died, among them also fell the king Viridomaro and for Rome on leveled the way in direction of Milan.
The Marcello Consul was given the honor of triumph for the overwhelming victory that will make the premises for the subsequent unification of the Italian territory under the sign of Rome.
Citizenship to all inhabitants of the peninsula will be formally granted only with the Lex Roscia of the 49 BC, extension of the most known Lex Papiria of the 89 BC, however Clastidium will politically lay the logical premises for the aforementioned normative definitions, probably carried out even before the 49 if only the Celts, in 218 BC, had not supported the Italic campaign of Hannibal in the name of an ephemeral charge that would break against the revived legions of Capua, meeting in Zama for the decisive battle, but this is another story.