The mountains and forests were a formidable obstacle to the Roman legions, and favored guerilla warfare, which makes conquest slow and laborious.
The most warlike of the Spanish tribes was the CELTIBERI, who occupied the interior of the peninsula.

They were always uncertain and intractable, continually breaking out into revolt.

In 195, Cato the elder put down a rebellion led by them.

He established more firmly the Roman power east of the Iberus.

He disarmed the inhabitants of this part of Spain, and compelled all from the Pyrenees to the Guadalquivir to pull down their fortifications.
Still the smouldering fires of rebellion were not extinguished, for, sixteen years later (179), we find TIBERIUS SEMPRONIUS GRACCHUS, the father of the famous Gracchi, as Governor of Spain, fighting the troublesome Celtiberi.