But there was a means of surmounting this difficulty.
Lucullus of his own accord attacked the western neighbours of the Arevacae, the Vaccaei, a Celtiberian nation still independent which was living on the best understanding with the Romans.

The question of the Spaniards as to what fault they had committed was answered by a sudden attack on the town of Cauca (Coca, eight Spanish leagues to the west of Segovia); and, while the terrified town believed that it had purchased a capitulation by heavy sacrifices of money, Roman troops marched in and enslaved or slaughtered the inhabitants without any pretext at all.

After this heroic feat, which is said to have cost the lives of some 20,000 defenceless men, the army proceeded on its march.

Far and wide the villages and townships were abandoned or, as in the case of the strong Intercatia and Pallantia (Palencia) the capital of the Vaccaei, closed their gates against the Roman army.
Covetousness was caught in its own net; there was no community That would venture to conclude a capitulation with the perfidious commander, and the general flight of the inhabitants not only rendered booty scarce, but made it almost impossible for him to remain for any length of time in these inhospitable regions.
In front of Intercatia, Scipio Aemilianus, an esteemed military tribune, the son of the victor of Pydna and the adopted grandson of the victor of Zama, succeeded, by pledging his word of honour when that of the general no longer availed, in inducing the inhabitants to conclude an agreement by virtue of which the Roman army departed on receiving a supply of cattle and clothing.

But the siege of Pallantia had to be raised for want of provisions, and the Roman army in its retreat was pursued by the Vaccaei as far as the Douro.