In book seven of the De Bello Gallico however, Caesar makes Vercingetorix say that trying to beat the Romans in pitched battles not only was detrimental, but near impossible, and that the Gauls should employ a tactic of scorched earth around the enemy, while constantly harassing the Romans with cavalry, and that’s exactly what they attempted to do. Vercingetorix knew the Gauls wouldn’t stand a chance in battle, and so acknowledged Caesar himself. They certainly weren’t the Romans’ equals. Gaul might have been a rich country, but not so all Gauls, some tribes were certainly richer than others, and none had a professional army like the Romans. I can easily imagine some Celtic soldiers fighting with nothing more than their kitchen knives. All ancient historians employ the terminology they’re more familair with to make their readers understand what they’re talking about, it doesn’t mean that Celtic armies employed a standard “phalanx” in their tactics. Their main MO was to charge against the enemy, rather than stand their ground, thus the ancient topos “they’re fierce soldiers, but they tire easily.” Caesar was an extraordinary general, and what he accomplished in Gaul only proves it, but we should never underestimate the impact quality troops can have in a campaing. Scipio Emilianus couldn’t beat some Celtiberians because his men were of abysmal capability, Sertorius couldn’t destroy Pompeius in open battle, despite being a far better general, because what Roman troops he had were lost by his lieutenants and the Iberians he had weren’t up to that task, and Agrippa had a very tough time with the Celtiberians and the Asturians because his troops were heavily undisciplined and wouldn’t follow his orders.