As the United States is finding out with some regularity, it is not easy to defeat an enemy that avoids battles. Targeting such an enemy is difficult not because it is technically complicated but because it is strategically of limited use: we can chase and sometimes hit a few targets, but these actions often have little impact on the wider problem, which allows the enemy simply to reappear elsewhere. War turns into a frustrating whac-a-mole game from the tactical to the strategic level, as the enemy vanishes on one street and reappears on another in a slightly different form and with a different set of tools. As the enemy spreads violence, or even just the possibility of violence, across a large geographic area, it sows instability undermining the authority of the ruling power.

The problem is not new.

Consider, for example, the war of Tacfarinas, a relatively forgotten and minor conflict described with keen insight by one of the world’s greatest historians, Tacitus, in his Annales. This war occurred in the first decades of the 1^st century AD in North Africa (15-24 AD), where Roman influence was spreading rapidly and rubbing against local tribes, who were naturally uneasy about a distant power extending its dominion over their territory. Rome was limiting the movement of local tribes, imposing taxes, and establishing boundaries and property rights on land, in the process forcing many of the locals to alter their semi-nomadic lifestyle. But regardless of the motivations for the rebellion, the way it took shape is instructive.

There were three distinct moments, characterized by a learning contest between the rebels and the Romans, in this conflict.

First, Tacfarinas, a member of a Numidian tribe, “deserted from service as a Roman auxiliary” (Annales, II:52) and began to gather around him marauders who were interested in looting. Like many other of the most lethal enemies of Rome (notably, the Germanic leader Arminius, a Roman citizen and soldier, who tricked a Roman commander, Varus, and three of his legions into marching into an disastrous ambush in the Teutoburg forest in 9 AD), Tacfarinas had learned martial skills in one of the many indigenous or auxiliary units that fought alongside Roman legions. Intimately familiar with Roman tactics and operations, he turned his expertise against his former ally. He quickly organized his own forces into formations and units, probably mimicking Roman legions, and became the leader not of a disorganized mob (inconditae turbae) but of the Musulamian people. More tribes joined Tacfarinas, who kept an elite part of his new army in encampments where he trained them in discipline and obedience (and armed them like Romans). Another part of the army, less Roman-like, was left to raid the surrounding territories and instill terror.

But this was a big mistake. The Numidians, thinking that Roman arms and organization made them peers of the legions, were eager to meet the Romans in battle. The Roman commanders were happy to oblige and easily routed Tacfarinas’s elite, Roman-like army. The rebels “were led to their defeat by the hope of victory.” (Annales, II:52). In the next encounter, near the river Pagyda, Tacfarinas managed to defeat a small Roman force that panicked, despite the valiant efforts of its commander Decrius. But after a brutal punishment of decimation, Roman forces stiffened up and in the succeeding clash (near the fort of Mala), despite numerical inferiority, they routed the Numidians.

The initial temptation of Tacfarinas was to mimic the Roman way of war and seek a decisive battle. It is likely that he thought that the inferior Roman numbers—after all this was the periphery of Roman power—would either result in a clear defeat or in a Roman retreat, both amounting to a strategic victory for him. The Romans, however, greatly valued the reputation of power, which could be maintained even in case of defeat: the mere fact of their willingness to stand up to enemies more numerous than their own legionaries was a sign that Rome would not give up easily control over a territory. In the end, the first encounters taught Tacfarinas the important lesson that Roman legions could not be replicated, even if one possessed the same armaments and a deep knowledge of their organization and tactics.

This leads to the second period of the conflict, characterized by Tacfarinas’s return to a more indigenous style of fighting. The Numidians were discouraged by the pitched battles and did not want to continue to put forts or cities under siege, two types of clashes in which the Romans had a clear advantage. Tacfarinas then, in Tacitus’s evocative phrase, spargit bellum (Annales, III:21); he began to scatter the war, sowing terror and disruption here and there, retreating and advancing, moving to the front and then to the rear of Roman forces. This is a succinct way of describing a hit-and-run tactic, or guerilla warfare. Instead of limiting the war to a battle along a clearly delimited front, or on a set piece of real estate, Tacfarinas spread the war everywhere. A relatively small rebellion became a ubiquitous war, engulfing a whole region and creating a series of challenges to the defending army.

Tacfarinas threatened everywhere, but the Roman army couldn’t be in all places, protecting every village and every road. Such a spargere bellum tactic stretched the defending imperial forces, tiring and frustrating them. It took some time for the Romans to learn that it was impossible to defeat a hostem vagum, a wandering enemy (Annales, IV:24). The Romans were tired and demoralized because they couldn’t find, and therefore couldn’t defeat, the enemy.

Perhaps more importantly from the political perspective, the Romans were ridiculed or mocked with impunity (impune ludifacabatur—Annales, III:21). Tacfarinas realized that he did not need to kill Roman soldiers to defeat them; he did not need tactical victories to achieve political ones. He could simply chip away at Rome’s reputation of power and its authority by mocking its forces militarily, showing that its mighty legions could not win against an enemy that they could not fix in place. And in a move that shocked and deeply upset Emperor Tiberius (of whom Tacitus was not a big fan), an arrogant Tacfarinas even sent envoys to Rome demanding land for himself and his forces, threatening a long war that would effectively be unsolvable (bellum inexplicabile—Annales, III:73).

The threat was worrisome. Surprising, plentiful, and yet small attacks threaten the order established by the imperial power. They empty it of meaning (the legal rules, the property rights, the system of taxation, the commercial systems) even though they leave its armature (the legions) intact. They make the security environment unpredictable, weakening the authority of Rome and then requiring an even larger and more costly intervention. That is why the Romans preferred to risk a military defeat early on (and often suffered one) in an attempt to forestall the spiral of rebellious violence and war with an enemy that could metastasize and reappear in new places. Once the seeds of violence have been spread, more and more tribes would join the rebellion, widening the belt of instability and demanding ever greater commitment and resources from the empire.

Virgil suggests a similar thought in the Aeneid, using the same verb (spargere) adopted by Tacitus. The Fury Allecto, whose task was to push the Trojans away from Italy and prevent them from establishing a foothold in Latium, claims that

(Virgil, Aeneid, VII, #638-641 in the Fagles translation)

Like Tacfarinas who was sowing war in North Africa (spargere bellum), Allecto would scatter arms around the fields of Latium (spargam arma per agros—Aeneid, VII, #551 in Latin). Such spreading of ubiquitous violence, an effective way of challenging existing powers’ monopoly on violence, and thus authority, was rightly feared by the Romans because a response to it required a protracted and painful period of adaptation.

The third period of the war with Tacfarinas forced the Romans to learn and adapt. The legions could not defeat an enemy that vanished as quickly as it appeared, and chasing it was arduous due to the topography, the enemy’s speed, and the lumbering nature of an imperial army. Legions, like many other imperial forces of ancient and modern times, were used to finding safety in their large numbers, well-managed logistics, and technical superiority. None of these features, however, were useful when the enemy was small, nimble, and avoided direct contact with the Roman legions.

The Romans had to become more like Tacfarinas’s confederation of tribes, and so it began to fight him with tactics not dissimilar from his (Annales, III:73). They divided their army into three groups: a mobile force to chase the marauding enemy, a more defensive group tasked with protecting the villages of local populations, and an elite group of soldiers whose task was to occupy strategic chokepoints, passes, and roads. Even these three groups were subdivided into smaller companies led by experienced centurions. The broad goal was to make the Numidians as afraid of a raid as the Romans were, while at the same time limiting their mobility by fortifying potential targets and key roads.

In effect, the Romans decentralized their forces, dispersing them to counter Tacfarinas’s ability to spread the war. An analogous situation is described by Tacitus in his Histories: under Vitellius the Danube region was in the midst of a prolonged rebellion, and the local commander decided to spread the army in the provinces (spargere per provincias—Histories, III:46), a wise move that would instill a modicum of peace. If the enemy makes war ubiquitous, the defender has to bring ubiquitous war back to him (with a corresponding effort to keep the locals safe everywhere). When the enemy is decentralized, the defense has to decentralize too; spargere bellum requires spargere legiones.

The problem for the Romans was the factor of time. Despite their brilliant tactical adaptations, they failed to alter their strategic and political mindset, continuing to think of the conflict as a period of time clearly defined by battles. Every small victory was greeted as final and decisive, and the army would retreat. After one such success (culminating in the capture of Tacfarinas’s brother), the Romans retreated “too soon for the interests of the province.” Moreover, Tiberius himself was eager to put this almost decade-long war behind him, allowing the local commander to be hailed by his troops as victor. The Emperor had other concerns that demanded his attention: North Africa was perhaps the least important of all imperial frontiers; a prolonged war made him look incompetent in front of the court; and a too successful commander of a large army could be a potential threat to his hold on power. It is not surprising that Tiberius recalled the 9^th Legion, and that nobody was willing to oppose his decision; the imperial court was more afraid of displeasing Tiberius than of facing the uncertainty of war (Annales, IV:23).

Of course, such a short-term attention span gave space and time for the enemy to “restart hostilities” (Annales, III:74), gathering even more forces in Mauretania (Annales, IV:23). The imperial power had the tendency to rush into declarations of victory, while the rebels had patience. Or, as a Taliban saying put it more recently: “NATO has all the watches, but we have all the time.”

On top of being a case of decentralized war (or a “skulking way of war” often adopted by inferior forces facing imperial might), the conflict between Tacfarinas and Rome is a great example of the competitive learning that underpins international rivalries: two strategic actors trying to outwit each other by assuming a fighting posture that exploit’s the enemy’s weak spots. Both sides committed mistakes: Tacfarinas’s early conceit that he could be a peer competitor of the Romans, Rome’s reluctance to accept the need for a long-term commitment to the war. But in the end, the winner, Rome, succeeded not because it was militarily more powerful (after all, the bulk of the forces had been withdrawn to protect other imperial frontiers), but because it managed to become more like the enemy, surprising the rebels in a lighting strike. Surrounded by legionaries and deprived of most of his soldiers, Tacfarinas ran into Roman spears, avoiding capture, a humiliating captivity, and a certain death in the end anyway. His death marked “the end of hostilities.” (Annales, IV:25)