Iskander Rehman, Iron Imperator: Roman Grand Strategy Under Tiberius (Bokförlaget Stolpe, 2024)
In AD 9, three Roman legions suffered a massacre in a region of Germania undergoing pacification. In the years that followed several attempts were made to capture or kill the German mastermind, Arminius of the Cherusci, who had shamed Roman honor at saltus Teutoburgiensis, the site of the Battle of Teutoburg Forest. All had failed. Then, in AD 17, the war chief of the rival Chatti nation, named Adgandestrius, approached the Romans with an offer he thought they could not refuse. Give him poison, he proposed, and he would kill Arminius. Without hesitation, the Roman commander-in-chief turned down the proposal. “It was not by deceit nor in secret,” he replied, “but openly and in arms that the Roman People took vengeance on their foes.”
It was a quaintly old-fashioned view of how the ancient world’s superpower should settle a score with a sworn enemy, yet it was in the long tradition of the Roman way of war: principled, fighting with integrity and courage, mano a mano. It was also entirely in character for the Roman supreme commander. In the event, the Cherusci themselves grew weary of their increasingly arrogant overlord. Arminius was murdered by one of his own people three years later.
The man who made that surprising decision to refuse assassination of an enemy combatant in AD 17 was Tiberius, Rome’s second emperor. His full official name, shown on coins and inscriptions, was “Ti. Caesar Divi filius Augustus filius” — which translates as “Tiberius Caesar, son of the God, son of the Revered One.” He was 55 years old when he became princeps, the title that his forebear had adopted to signify his preeminent role, meaning “First Man.” Tiberius’ rise to the highest position in Roman society in AD 14 was partly by happenstance, partly by design, partly by dint of achievement, and quite unexpected. Reigning between the famous emperor Augustus and infamous Caligula, Tiberius is often underrated and his achievements generally understated. A fine general with a track record for success on the battlefield, it is his 22 years of rule for which he is best known. While researching my own biography of Tiberius, it became very clear to me that his reputation as a wise administrator and capable commander-in-chief has been distorted by later historians, novelists, playwrights and film producers. They have repeated, uncritically, exaggerated claims that he was a tyrant who used treason trials to eliminate political enemies and vituperous allegations that he was a monster who indulged in sexual depravity. He was not Augustus’ first choice for successor, but circumstances demanded that he make Tiberius his heir. He deserves to be studied fairly but critically, because the decisions he made concerning Ancient Rome’s statecraft and diplomacy ensured that its empire would last for centuries. How he did so is the story that Iskander Rehman admirably explores in Iron Imperator: Roman Grand Strategy under Tiberius. The handsomely produced book is written in an easy to understand style that deftly uses the ancient sources to explain this complex Roman in the context of his times.
Guardian of the Empire
It was not evident until quite late in his life that Tiberius would become the preeminent man in Rome. He was born Tiberius Claudius Nero on 16 November 42 BC. As a member of the Claudian clan, he bore its weighty reputation forged by a long line of highly successful war fighters and political leaders on both his father’s and his mother’s side. They had fought against some of Rome’s toughest opponents, notably the Gauls and Carthaginians, and had won battle honors and even the distinction of full triumphs; they had also held all the offices of state of the Res Publica, the Commonwealth of the Senate and People of Rome, some becoming consuls after whom the Romans named their years.
Roman society and politics were military in character. A magistrate’s imperium — meaning ‘command’ — was essentially a military power, granting him (it was always a man who wielded it) the authority to hold a state-sanctioned position and carry out his duties. Having completed the assignment, often of just a year’s duration, he could be held to account by his peers in the Senate and even prosecuted and face banishment from Rome if found guilty. Over a career, an ambitious patrician like Tiberius would serve the Res Publica alternating between civil and military postings, earning prestige and influence, and opportunities for augmenting his wealth with each promotion.
When he reached the age of 16, Tiberius’ career began. Accompanying his stepfather Augustus, he was assigned to one of the legions on campaign then completing the conquest of the Iberian Peninsula. He was appointed as a military tribune “of the broad stripe.” In this position he was the second most important officer. There were no military academies in Ancient Rome. Rather, a young man learned military science and the art of command through observation and by doing. In Northern Spain, Tiberius would have been privy to decisions about strategy and tactics. In charge of a team of five junior tribunes “of the narrow stripe” himself, he learned how those orders were executed in practice.
Back in Rome two years later, Tiberius became quaestor, responsible for managing the corn dole and investigating abuses at the workhouses or slave prisons in Italy. He was then appointed lead prosecutor in the court handling accusations of treason in a high-profile case involving a conspiracy to assassinate Augustus. The case ended when the accused attempted to escape, but was betrayed and executed.
Augustus next entrusted Tiberius, now 22, to lead a mission to negotiate a peace treaty with Rome’s nemesis, Parthia. Recognizing that the Romans could not beat the Parthians, Augustus chose diplomacy to secure the empire’s eastern border. Having successfully negotiated a treaty, he returned to Rome with Augustus, and a grateful Senate was waiting for him with triumphal ornaments. He was also rewarded with the prestigious position of chief magistrate for the administration of justice in Rome.
Five years later, Tiberius became governor of the three Gallic provinces. This was the region conquered by Julius Caesar. It still had something of a Wild West aspect to it as native peoples slowly assimilated the Roman way of life. In the adjacent Alpine Mountain range, Celtic tribes harassed Roman traders traveling from Italy to Gaul. At Augustus’ request, Tiberius fought side by side with his younger brother, Nero Claudius Drusus (not to be confused with Nero, the infamous emperor). In a single summer campaign, the brothers successfully completed their mission and the peoples of Raetia, Vindelicia, and Noricum were assimilated into the Roman empire, even providing auxiliary troops who served with the Roman army.
In recognition of his achievements, Tiberius became consul, one of the two most important magistrates in the Res Publica, with Quinctilius Varus as his colleague. Still not yet 30, Tiberius had clearly demonstrated a talent for governance, diplomacy, and warfare. After completing his consulship, for the next five years he would conduct operations to pacify the obdurate tribes of Illyricum in the Western Balkans. His brother, meanwhile, prosecuted a war of choice to defeat the belligerent peoples across the Rhine River. When Nero Drusus died unexpectedly in 9 BC, Tiberius assumed responsibility for concluding the offensive and led expeditions against the Germans until AD 5. These campaigns, like the one in the Iberian Peninsula, were wars of attrition. For his victories he earned a full triumph, the highest honor given to a victorious military commander.
Standing between Rome and its total conquest of Germania were the Marcomanni, a coalition led by Maroboduus. He had lived among the Romans, but had returned to his own people across the Danube and now commanded a formidable army. In AD 6, Tiberius mobilized an immense army to invade his kingdom. The legions had already marched into the area when news arrived of a rebellion among the auxiliary troops recruited from tribes in Illyricum. Non-citizen infantry and cavalry represented almost half of Roman military manpower. The revolt quickly gained traction. Fearing that Italy could be at risk, Tiberius hastily concluded a treaty with Maroboduus and marched south to deal with the rebellion, spending the next four years warring in the Dinaric Alps and lowlands. Victory was finally secured in AD 9, but the joy of it vanished when Tiberius received news of the disastrous defeat of Roman general Publius Quinctilius Varus in the Battle of the Teutoburg Forest.
Tiberius did not act impulsively or rashly. He ordered his adopted son, Germanicus to rally the garrisons on the Rhine and to hold the line against an anticipated invasion from the north while Tiberius went to Rome to strategize with Augustus. A whole year passed before Tiberius led an army across the Rhine, demonstrating that the Romans could still come and go as they pleased. He ended the mission with games to mark Augustus’ birthday on Sept. 23. Germanicus was appointed governor of Gaul and tasked “to wipe out the disgrace of the loss of Quinctilius Varus”.
By AD 14, Tiberius had spent decades in military service on what Rehman aptly describes as “the ragged edges of the empire,” from the Ebro to the Euphrates, and the Drilon to the Danube. His soldiers appreciated his “stern but fair” approach to command and he had earned their devotion. He put his men’s safety first, ensuring all precautions were taken, even making available his own carriage and physician to provide for their care and recovery when wounded on the battlefield. Early in his reign, Augustus planned for others to succeed him. However, sickness had prematurely ended the lives of Augustus’ nominees. In AD 4, Tiberius became his heir. When the old emperor died ten years later, Tiberius had accumulated all the legal powers to assume leadership of the Res Publica as “First Man.”
Iron Emperor
Upon Augustus’ death, the Senate appealed to Tiberius to take his place and become princeps. The moment the news of Tiberius’ acceptance reached the legions on the Danube and Rhine, many of them mutinied. At issue were pay and conditions. Tiberius sent his own son, Drusus, to the Danube, while Germanicus went to the summer camps of the Rhine Army. The two emissaries heard the soldiers’ complaints. They agreed to reduce their years of service from twenty years to sixteen and to increase their stipends. Discipline was enforced: for murdering their officers, the ringleaders were dealt with severely. The brothers proved loyal to their father, and their swift actions averted the crisis from spreading. Tiberius had survived the challenge to his position.
The largest expenditure in the state budget was the army. Augustus created the professional, standing army for which the Romans are famed. Recognizing that their political position relied on the unwavering support of the legions, Augustus and Tiberius set up a separate military treasury (Aerarium), initially funded with their own cash and later by taxes on consumption, to ensure there was sufficient money in the budget. In one of his earliest acts, in AD 15 Tiberius reinstated the longer service term of 20 years for legionaries to reduce the burden of early retirements on the Aerarium. Recognizing the wisdom of his insight, later emperors would extend the term further to 25 years.
Concurrently, Germanicus was permitted to seek and capture Arminius. He led a task force from the Rhine and for two years, AD 15-16, engaged the Germans. Survivors of Teutoburg took him to the site of the massacre and he oversaw the burial of the bones of his countrymen, movingly described in a chapter of Tacitus’ Annals. But Arminius was not so easily caught. Despite the Romans winning three set-piece battles, the German war chief evaded capture. When Germanicus requested a troop surge to escalate the war for another season in AD 17, Tiberius refused him, writing in his letter, “He had himself been sent nine times by Augustus into Germania and had done more by policy than by arms.” Germania was to be abandoned — for good.
In Rome, Tiberius encouraged the Senate to re-assume its historical control of regulating commerce, maintaining diplomatic relations, and supervising religious matters. Its appetite for acting proactively had, however, already been dulled by 40 years of Augustus’ rule. There were many times when Tiberius was frustrated by its apparent unwillingness to lead on political matters, which I recount in my own book. Nevertheless, he personally attended to his primary responsibility for ensuring the security of the empire as imperator: Derived from imperium and meaning “commander,” it was an honorific title granted by troops who acclaimed their leader for bringing them victory on the battlefield. Augustus had shamelessly adopted the title as his first name in the 30s BC and, in time, it would connote what we understand by “emperor.”
The title of Rehman’s book, Iron Imperator, relates to a line in a poem by an unknown protester preserved by Suetonius:
You, O Caesar, have altered the golden ages of Saturn;
For while you are alive, iron they ever will be.
The “golden ages” here refers to the era under Augustus. Between 27 BC and AD 14, his legions had completed the conquest of the Iberian Peninsula and the Alps, pacified the Western Balkans, and even brought barbarian Germans under Roman imperium. The Roman Treasury swelled with the abundant proceeds of the sale of war spoils and the city of Rome was beautified, transformed, as he claimed, from one of clay into one of marble — even if it was really only a marble veneer over a brick and concrete core. Yet many an aristocrat of the old families, who had done well after the Punic Wars and survived the recent civil wars were also critics of Rome’s first princeps.
A “traditionalist by nature,” Tiberius was more cautious in spending both Roman blood and treasure. Where Augustus had embarked on expensive wars of choice, Tiberius mostly executed wars of necessity, always preferring diplomacy with foreign foes provided it was backed with force of arms. These were the lessons he had learned over a lifelong career in the army and politics. Thus, during his reign the profits of war were meagre, which meant raising taxes to pay for the ongoing expense of the Roman Army whose posture was now largely defensive. Fiscally conservative, Tiberius favored the maintenance of existing structures; in contrast to Augustus, his additions to the city’s inventory of new buildings were few, notably the Temple of Castor and Temple of Concord. Tiberius set high standards for men serving in public office, especially among those sent out to govern the provinces of the sprawling empire. Where Augustus rotated his provincial legates every three years, Tiberius kept them in place for extended periods, even decades in some cases. He held these men accountable for their actions, and they did not like it. He advised his provincial governors that “it was the part of a good shepherd to shear his flock, not skin it.” When provincials brought cases against proconsuls for cruelty or extortion, Tiberius urged the Senate to harshly punish these semi-autonomous representatives of Roman power. Many an aristocrat of the old families, who had survived and thrived under Augustus, were now critics of Rome’s second princeps too.
Rehman titles the second part of his book, “The Reluctant Ruler.” The moniker is one several historians and writers have used. It is an assessment predicated on a reading of the Roman historians Tacitus’ and Cassius Dio’s accounts of the debate in the Senate House about who would be princeps after Augustus’ death. Tiberius was not Augustus’ first choice, but in August AD 14 he was the best one. Tiberius is reported as suggesting the responsibility of leading the Roman state was too large for one man and “the business of the Res Publica would be more easily carried out by the joint efforts of a number.” Tacitus read hypocrisy into Tiberius’ words, but the reality was that he, better than anyone alive, knew the complexity of ruling a sprawling empire. When Augustus founded the imperial system, he gave little thought to the mechanics of the handover of power. It was left to Tiberius and the Senate to work out the details. The Senate believed he would gladly accept the role of princeps without contest. However, Tiberius used that debate to negotiate the terms of his appointment. As I explain in my own book, I do not see this as reluctance, but as smart politics on Tiberius’ part. Significantly, Tiberius gave the Senate a get-out clause: he would resign any time they asked him to. The Senate never invoked it. As Tiberius is reported to have said eight years later, “Something greater and loftier is expected of a princeps, and while everybody takes to himself the credit of right policy, one alone has to bear the odium of every person’s failures.”
Roman Grand Strategy under Tiberius
The subtitle of Rehman’s biography is Roman Grand Strategy under Tiberius. Tiberius inherited a system of administering the empire negotiated between Augustus and the Senate in 27 BC, which saw the provinces divided between them. Augustus’ duty was to pacify the war-torn regions of the empire and, once he achieved it, he was to turn them over to the Senate to govern through proconsuls chosen from among their members by lot each year. The legions were variously engaged in wars of necessity — to crush rebellions within the borders (limes) of the empire — or wars of choice — to eliminate external threats on or beyond them. Tiberius himself played a significant role in establishing the resulting Pax Augusta (or Pax Romana). For Augustus, “peace, [was] secured by victory.”
To the extent that Augustus had a grand strategy, it was to leverage war or the means of waging it as an instrument to secure his political power as princeps. After all, under his control were the 28 legions (25 after Teutoburg), numerous units of auxiliaries, and regional fleets representing 220,000 to 300,000 men at arms. The poet Virgil articulated the strategic imperative succinctly as imperium sine fine, “command [or empire] without end.” Indeed, Tiberius’ life in the military was a manifestation of it. Only in his final decade, after years of spilled blood and squandered treasure, did Augustus advocate for containment. Before his death, Augustus had offered Tiberius clear counsel, “that the empire should be confined to its present limits.” Roman historian Tacitus explains, “The ocean and remote rivers were the boundaries of the empire — the legions, provinces, fleets, all things were linked together.” For Tiberius, the precept — in effect, his grand strategy — was to be imperium cum fine, “command [or empire] with limits.”
Through the 22 years of his reign (AD 14 to 37) Tiberius followed the spirit, if not always the letter, of Augustus’ advice. The disposition of the legions and auxiliary infantry and cavalry units was as he had inherited it; he almost certainly had a major say in their deployments before his accession. When a Roman auxiliary named Tacfarinas led a rebellion in Africa, a province governed by a proconsul, Tiberius worked with the Senate to restore order; the campaign was a protracted one (AD 17 to 24), but ultimately successful, with three Roman commanders being awarded triumphs. He respected the chain of command and trusted his officers to carry out their duties without being told to. Thus, local commanders responded to rebellions among the Gallic Aedui and Treveri (AD 21), the German Frisii (AD 28), the Thracians (AD 21), and slaves in Italy (AD 24), all confident that their commander-in-chief, Tiberius, had their back. When the Parthians sought to upset the peace in neighboring Armenia, a buffer state between the empires, Tiberius sent troops to support a pro-Roman king (in AD 35 and 36) and so restore the status quo ante of 20 BC. Pragmatism defined Tiberius’ policy on war and peace. In Rehman’s assessment, “retrenchment” was the main thrust of that policy. He describes Tiberius’ “Germanian policy” as “a combination of masterly inactivity and shrewd proxy management,” noting with respect to Rome’s dependence on allies, client kingdoms and auxiliaries notably in the East, that “Tiberius proved singularly adept at alliance management and great power competition.”
Applying the insights gleaned from a study of Tiberius’ approach to war and peace to modern situations is a tricky task. If history does not actually repeat itself, studying it is, nevertheless, instructive to the present. Rehman is an advocate for comparative history and the analysis of protracted great power war throughout history to distil the key determinants of strategic performance. He argues that many of the issues raised by Roman historians about Augustus and Tiberius “remain strikingly relevant to today” and especially for “contemporary discussions of American grand strategy.” Rehman posits that today’s focus is the “decline in US relative power” and “the emergence of China as a redoubtable near-peer competitor.” He evokes the writings of Roman historian Sallust (86 to 34 BC). His thesis is that Sallust criticized “late Republican Rome’s descent into acrimony and its inability to develop a clear strategic focus.” The Romans rooted their domestic and foreign policies in their ancestral values, which reminds “the American people that their nation’s struggle lies with the People’s Republic of China’s ideologically driven revisionism.” Even with its prowess in war fighting, the Rome of the Caesars could manage only one major conflict at a time. The Romans were forced to negotiate with Maroboduus when auxiliaries revolted in Illyricum, but the decision:
telegraphed Rome’s inability to address multiple major military challenges in concert may have prompted opportunistic attacks in Germania (the Teutoburg massacre), buoyed the propaganda of insurgents in the vein of Tacfarinas or Sacrovir [of the Aedui], and prompted attempts at the formation of countervailing coalitions.
Rehman notes that the first Trump administration’s National Defense Strategy outlines a doctrine in which the United States prevails in one conflict while deterring aggression elsewhere. America should never over-commit its limited military resources. He wonders whether there are “insights that can be derived from Rome’s rich experience with surrogate or indirect warfare, particularly at a time of increased zone competition and proxy warfare.” In the 1st century, the Romans came to rely on allies, client kingdoms and auxiliary troops; they fully understood the benefits and risks of these arrangements and that such relationships had to be sustained over long periods. Thus, allied German tribes and the kingdom of Armenia formed buffer zones between external threats and the Roman border, often requiring intervention to maintain the peace. Supporting Ukraine with matériel as it struggles to maintain its integrity and independence from Russia might represent such a buffer between NATO and the Russian Federation in the 21st century.
Rehman may actually understate Tiberius’ active involvement in the military as emperor and the extent to which he concerned himself with operational details as supreme commander, themes that I explore in my own book, Tiberius: From Masterly Commander to Masterful Emperor of Rome. Upholding standards greatly mattered to him. While he respected the chain of command, nevertheless he criticized his subordinates for failing to recognize exceptional performance and valor by not issuing decorations to deserving troops when he had given them the authority and discretion to do so. He expressed his frustration to the Senate that he personally had to persuade men of quality to serve as senior officers in the army. Addressing declining levels of recruitment of the regular men, he complained to the Senate about falling standards when those who willingly enrolled in the ranks were not of the best ability or fitness. Even while he lived on the island of Capri, swift ships of the fleet from Misenum delivered reports from his legates and relayed back his replies. A field commander to his core, Tiberius understood the dictum articulated four centuries later by Vegetius: “Who wants peace prepares for war.”
Where Augustus acted as “a power-hungry counterrevolutionary,” Rehman sees Tiberius’ “more prudent brand of statecraft.” A lifetime on active duty had crafted his outlook. Yet, by heeding Augustus’ advice and implementing sound military and political policy decisions informed by his own judgment borne out of experience, his successor ensured that the Roman Empire would endure for hundreds of years. Tiberius would never be popular with his peers in his lifetime and even less so in death. He was criticized — unfairly in my opinion — by Roman historians for his apparent lack of ambition to expand the dominions of Rome. As I explain in my own book, better than anyone, as a commander who put men in harm’s way, he ran the calculus: Often the gains did not outweigh the cost. After he died on 16 March AD 37 — some Roman accounts say he was murdered — he became a figure of derision. Yet time would prove him right. Rehman astutely concludes:
There was therefore an increasingly shared assumption that the Roman Empire had reached its natural perimeter, and that where those vague, porous boundaries slowly dissipated into mysterious, exotic, and primeval lands, there remained little that could —or should — be conquered. The enduring loneliness of Tiberius’ genius resides, perhaps, in the fact that he uncovered the uncomfortable truth earlier than most.
Lindsay Powell is news editor of Ancient History and Ancient Warfare magazines. As a historian, he writes about commanders, campaigns and conflicts of the Ancient World and is the author of 14 books, including Marcus Agrippa and Augustus at War. His latest book is Tiberius: From Masterly Commander to Masterful Emperor of Rome (Pen and Sword Books, 2025). He can be followed on X: @Lindsay_Powell.
Image: Wellcome Images via Wikimedia Commons
