But were they (legions that is) at full strength? Highly unlikely.
That's impossible to know with any degree of certainty. But just looking at the rough numbers, they seem credible, that's all. Catulus in command of a consular army-sized force is perfectly okay with the size of the armies that the Romans mobilized regularly each year for a new compaign during the Republican era; the size of Marius' force is trickier, but taking into account that he was
dictator and that he'd just been able to crush the Teutones at
Aquae Sextiae, it seems also quite plausible to me (he could even have had Gallic allies from Narbonensis with him to make up for the losses he could've suffered in legionaires and Italic
socii).
The real problem lies in estimating the size of the Cimbrian force, both its effective number of warriors and the total numbers of the whole people, adding the non-combatants. And what I find really hard to believe is the ridiculously low number of Roman casualties, as the Cimbri did not panick and flee in the first stages of the battle; the only way such a low count could perhaps be remotely credible would be if the Roman sources counted as losses only those of Roman citizens, leaving out of the accounting the
socii and allies. As for the losses of the Cimbri, who knows. We can be reasonably sure that they probably had more men than Catulus in order to force him to retreat several times, but given the sudden stop in the Roman retreat after he joined forces with Marius, I'd be willing to bet that the combined Roman army had more men than the Cimbri, and that it was Marius and Catulus who forced them into battle, with the knowledge that now they enjoyed a numerical superiority; as the Cimbri were encumbered by the non-combatants who accompanied them, they couldn't do what Catulus had done and retreat before the Romans, so probably they had been lured into a trap by the more mobile Roman forces, which now proceeded to exploit their superiority in numbers.
If I had to take a guess, I'd give the Cimbri an armed strength of between 30,000 and 40,000 men, stronger than Catulus but weaker than the combined Roman armies. If we multiply 30,000 by a factor of four (which as I said before is completely arbitrary) to account for women, children, sick and old men and slaves, we'd reach a total mass of 120,000 people, near Livius' numbers. And I'd like to know how they would've managed to feed such a horde while crossing the still snowed Alps, taking into account that Raetia and Noricum weren't exactly agricultural powerhouses at the time. The Romans, with their organized logistics, could rely not only on local resources, but also on grain carried by sea and unloaded in the Ligurian ports in their rearguard, from agricultural rich regions like Sicily, Campania or Africa. Also, the Romans wouldn't have killed all of the Cimbri: most of them (especially the non-combatants) would have been captured. Let's bear also in mind, when talking about the butcher's bill, that sick, injured and old people were of no use for the Romans as slaves, so probably they slaughtered them all
en masse at the site of the battle. Taking all this into consideration, the total number of Cimbrian dead given by Florus (65,000) seems to me, in my opinion, relatively plausible.
Of the whole war between Rome and the Cimbri and Teutones, the "strange" battle is not Vercellae, but Arausio, because if the numbers of the Roman army given by the ancient sources are correct (80,000 men) and it really was a total disaster with few survivors, it's puzzling to understand how did the Romans manage to get beaten that badly, because I'm almost completely sure that even adding the warriors of both the Cimbri and Teutones, they can't have added up to 80,000 men (without a proper logistic train and long-distance supply system like the Romans had).
