If Roman military intervention in the east was sporadic in the 2nd century, campaigning in northern Italy and Spain was nearly continuous. During Hannibal’s invasion of Italy, the Insubres and Boii, Gallic peoples in the Po valley, had joined the Carthaginians against Rome. In 200 the Gauls and Ligurians combined forces and sacked the Latin colony of Placentia in an attempt to drive the Romans out of their lands. In the following years consular armies repeatedly attacked the Gauls. In 194 Lucius Valerius Flaccus won a decisive victory over the Insubres, and in 192 the leading Boii under severe pressure went over to the Roman side, signaling the coming defeat of their tribe. Following their victories, the Romans sent thousands of new colonists to the Po valley to reinforce the older colonies of Placentia and Cremona (190) and to establish new colonies, notably Bononia (189) and Aquileia (181).

During the same period the Romans were at war with the Ligurian tribes of the northern Apennines. The serious effort began in 182, when both consular armies and a proconsular army were sent against the Ligurians. The wars continued into the 150s, when victorious generals celebrated two triumphs over the Ligurians. Here also the Romans drove many natives off their land and settled colonies in their stead (e.g., Luna and Luca in the 170s).

As a result of the Second Punic War, Roman legions had marched into Spain against the Carthaginians and remained there after 201. The Romans formalized their rule in 197 by creating two provinces, Nearer and Further Spain. They also exploited the Spanish riches, especially the mines, as the Carthaginians had done. In 197 the legions were withdrawn, but a Spanish revolt against the Roman presence led to the death of one governor and required that the two praetorian governors of 196 be accompanied by a legion each. The situation was serious enough for the consul of 195, Cato the Censor, to be sent to Spain with two legions. From Cato comes the earliest extant firsthand account of Roman conquest. His comments show that he prided himself on his bravery and lack of greed as compared with other Roman commanders. Yet his narrative must overstate the extent and decisiveness of his success because fighting persisted for years to come, as later Roman governors sought to extend Roman control over more Spanish peoples—the Celtiberi of northeastern Spain, the Lusitani of modern-day Portugal, and the Vettones and Vaccaei of northwestern Spain. In 177 Tiiberius Sempronius Gracchus celebrated a triumph over the Celtiberi. The size of the Roman forces was probably then reduced from four to two legions, and from 173 to 155 there was a lull in the regular campaigning. During these decades Spanish peoples brought complaints to Rome about corrupt governors.

Annual warfare resumed in Spain in 154, being perhaps in part a violent reaction to corrupt administration, and dragged on until 133. Labeled a “fiery war” (really wars), these struggles acquired a reputation for extreme cruelty; they brought destruction to the native population (e.g., 20,000 Vaccaei were killed in 151 after giving themselves up to Lucius Licinius Lucullus) and made recruiting legionaries in Italy difficult. In Further Spain the Lusitanian leader Viriathus enjoyed some successes, including the surrender of a Roman army in 141–140 and a favourable treaty with Rome, but the next governor of the province, Quintus Servilius Caepio, arranged for his assassination in 139. Two years later in Nearer Spain, the Numantines also forced the surrender of an army under Gaius Hostilius Mancinus; the Senate later disavowed the agreement of equal terms and handed Mancinus, bound and naked, over to the Spaniards to absolve themselves of responsibility before the gods. The wars in Spain were brought to a conclusion in 133 by Publius Cornelius Scipio Aemilianus, who took Numantia after a long siege, enslaved the population, and razed the city.

It was Scipio Aemilianus (born 185/184) who in the previous decade had imposed a similar final solution on Carthage in the Third Punic War (149–146). After the Second Punic War, Carthage had recovered to the point that in 191 it offered to repay the remainder of the 50-year tribute of 200 talents per year in one lump sum. Rome’s refusal of the offer suggests that beyond its monetary value the tribute had the symbolic importance of signifying subjection. Carthage’s neighbour, the Numidian king Masinissa, had been granted as a reward for his support of Rome at the Battle of Zama his paternal kingdom and the western Numidian kingdom ruled by Syphax. During the next half century Masinissa periodically tried to exploit his favour in Rome by encroaching on Carthaginian territory. Initially, the Carthaginians submissively sought the arbitration of Rome in these disputes, but more often than not Roman judgment went in favour of Masinissa. After a series of losses, the Carthaginians in 151 decided to act on their own and raised an army to ward off the Numidian attacks. When a Roman delegation observed the Carthaginian army raised in breach of the treaty of 201, Rome was provided with the casus belli for a declaration of war in 149; Polybius, however, claims that the Senate had decided on this war “long before.” The elderly Cato had been ending his speeches in the Senate since 153 with the notorious exhortation that “Carthage must be destroyed.” Carthage desperately and pathetically tried to make amends, executing the generals of the expedition against the Numidians, surrendering to Rome, and handing over hostages, armour, and artillery. Only then did the Romans deliver their final demand: Carthage must be abandoned and the population moved to a new site inland. Such extreme terms could not be accepted.

The war against Carthage, with its prospects of rich booty, presented no recruiting problems for the Romans: huge land and naval forces were sent out under both consuls of 149, Lucius Marcius Censorinus and Manius Manilius. The imbalance of resources meant that the outcome was never in doubt, but the fortifications of Carthage delayed the Roman victory. The young Scipio Aemilianus was elected consul for 147, and by popular vote he was assigned the task of bringing the war to an end. He blockaded the city by land and sea, inflicting terrible suffering. Finally, in 146, the Roman army took Carthage, enslaved its remaining 50,000 inhabitants, burned the buildings to the ground, and ritually sowed the site with salt to guarantee that nothing would ever grow there again. Carthaginian territory was annexed as the province of Africa.

Explanations of Roman expansion

As one of the decisive developments in western history, Roman expansion has invited continual reinterpretation by historians. Polybius, who wrote his history in order to explain to other Greeks the reasons for Roman success, believed that after their victory over Hannibal the Romans conceived the aim of dominating all before them and set out to achieve it in the Second Macedonian War. If one accepts the Roman view that they fought only “just wars”—that is, only when provoked—then Roman conquest emerges as “one of the most important accidents in European history,” as Rome had to defend itself from threats on all sides. Historians have suggested other motives for empire, such as a desire to profit from war, an interest in commercial expansion, or a love of the Greeks, who asked for protection against Hellenistic monarchs.

Major historical phenomena of this kind rarely receive final, decisive interpretations, but several assertions may be ventured. Some of the interpretations are anachronistic impositions on the ancient world. Ancient testimony, for example, gives no support to commercial or mercantile explanations. Cultural and economic interpretations seem more appropriate. Roman culture placed a high value on success in war: virtus (courage and qualities of leadership) was displayed, above all, in war, and the triumph, a parade through Rome celebrating a major victory over an enemy, was the honour most highly prized by the senatorial generals who guided Roman decisions about war and peace. Moreover, these leaders, and the whole Roman people, were fully aware of the increasing profits of victory; in the 2nd century commanders and soldiers, as well as the city itself, were enriched by the glittering booty from Africa and the Greek East.

Yet, it is rightly pointed out, Roman intervention in the East was sporadic, not systematic, and the Romans did not annex territory in the Balkans, Anatolia, or North Africa for more than 50 years after their initial victories. The latter point, however, is not telling, since the Romans regarded defeated states allied to them as part of their imperium, whether or not they were under Roman provincial administration. The sporadic timing of the wars would seem to support the Romans’ claim that they only reacted, justly, to provocations. But attention to the individual provocations should not blind the historian to the larger pattern of Roman behaviour. From 218 the Romans annually fielded major armies decade after decade. Rome was able to go to war every year in response to provocations only because it chose to define its interests and make alliances farther and farther afield. Polybius, as noted, reveals how the Romans were the masters of manipulation of circumstances to force opponents to behave in a way they could interpret as provocative. Therefore, the Roman interpretation of “just wars” and the Polybian interpretation of a universal aim to conquer need not be contradictory. The concept of “just war” may have justified any given war but does not explain the perpetual Roman readiness to go to war. For that the historian must look to Polybius’s universal aim or to general political, social, economic, and cultural features of Rome. Finally, it must be remembered that in some instances it was clearly the Roman commander who provoked the war in order to plunder and to win a triumph (e.g., Licinius Lucullus, governor of Nearer Spain, in 151).