Tiberius Claudius Nero, born 42 b.c.e, was Rome’s second emperor, after Octavian — Julius Caesar’s grandnephew and adopted son, later known as Augustus, Rome’s first and greatest emperor — and before Gaius (Caligula), Rome’s maddest and doubtless worst emperor. Of Rome’s emperors, Tiberius, who led Rome between 14 c.e. and his death in 37 c.e., has the least settled reputation. Today, nearly two millennia later, scholars have still been unable to decide on the exact quality of his leadership. He is, as Iskander Rehman notes early in Iron Imperator: Roman Grand Strategy under Tiberius, “perhaps one of the most enigmatic figures of antiquity.”

Tacitus wanted to think the worst of Tiberius and relied on rumor to establish his connection to the death of his enemies and potential opponents. At the close of the sixth of his Annals, Tacitus holds that Tiberius’s character “had its distinct periods.” He refers to his “crafty assumption of virtue,” cites the infamy earned by his cruelty, and claims that he “finally plunged into every wickedness and disgrace when, fear and shame being cast off, he simply indulged his own inclinations.”

As for those inclinations, they are highlighted in Suetonius’s account of Tiberius in his The Twelve Caesars. Suetonius notes some of Tiberius’s generous acts. He provides a physical description of him: “Tiberius was strongly and heavily built, and above average height. His shoulders and chest were broad, and his body perfectly proportioned.” But what stands out in Suetonius’s account is Tiberius’s perversions at his retreat in Capreae, as the island of Capri was then known.

“On retiring to Capreae he made himself a private sporting house, where sexual extravagances were practiced for his secret pleasure,” Suetonius writes. He adds: “Some aspects of his criminal obscenity are almost too vile to discuss, much less believe.” Which doesn’t stop Suetonius from discussing them. “Imagine training little boys, whom he called his ‘minnows,’ to chase him while he was swimming and get between his legs to lick and nibble him. Or letting babies not yet weaned from their mother’s breast suck at his breast or groin — such a filthy old man had he become.” Suetonius ends his account of Tiberius by writing: “The first news of his death caused such joy at Rome that people ran about yelling: ‘To the Tiber with Tiberius!’ and others offered prayers to Mother Earth and the Infernal Gods to give him no home below except among the damned.”

A more balanced view of Tiberius is provided by Theodor Mommsen, the great 19th-century historian of antiquity. “Tiberius was a superior officer and administrator,” Mommsen writes. “As a ruler, however, he lacked self-confidence, stopping timidly in the tracks of Augustus in both domestic and foreign policy.” He was also “the most constitutional monarch Rome ever had.” His reign was “an eminently peaceful one.” He was especially able at financial administration — so able that “later rulers saw in him a model they could not live up to.” He was sedulous in investigating complaints throughout the empire, and “saw to the security of highways and the suppression of robbery in Italy, where brigandage had been on the rampage in the aftermath of the civil war.” Mommsen concludes: “If anyone could have the sense of having ruled well it was Tiberius, and yet he was rewarded for it by bitter hatred. No wonder his misanthropy was so overwhelming. He had much in common with Frederick the Great.”

Tiberius’s was not a life without suffering. Not long after being adopted by Augustus, who had married his mother, Livia, he was forced to divorce the wife he loved and marry Augustus’s slutty daughter Julia, who was later sent into exile for her sexual antics. Tiberius was eventually chosen as Augustus’s successor, but only after more appealing candidates had died either in battle or by natural causes. After having appointed Tiberius his successor, Augustus is quoted by Suetonius as remarking: “Ah — an unhappy Roman people, whose fate is to be ground up by this slow devourer’s jaws.”

Among the least ambitious of Roman emperors, Tiberius seemed content to remain a general, leading his legions. At one point, he in effect exiled himself to the island of Rhodes, where he remained for fully seven years — not, one would think, a good career move. When in office, he eschewed the title of emperor. Unlike his predecessors, Julius Caesar and Augustus, he asked that no month be named after him. Had he not done so, Labor Day today would fall on the first Monday in Tiberius.

In his Iron Imperator, Rehman is less interested in evaluating Tiberius’s character than in tracing his military and political actions when emperor. In the introduction, Rehman refers to “the troubled legacy of . . . one of Rome’s most overlooked, and perhaps misunderstood, rulers,” and adds that “the portrait that surfaces from the palimpsest of historical accounts is one of unabashed and frustrating complexity — one whose contours can prove exceedingly difficult to discern, let alone understand.” In the final paragraph of his book, Rehman quotes the historian G. P. Baker writing of Tiberius that he “has always been, and he remains, the greatest psychological problem in history. He is Hamlet and Lear and Othello rolled into one; and he is more than this.”

Iron Imperator is not a traditional biography. Rather it is intended as a work of “applied history.” Rehman is studying Tiberius for what he — and we with him — can learn about our own contemporary policy decisions. “This book will seek,” Rehman writes, “in particular, to gauge whether the Tiberian era — during which the international system’s leading power seemingly succeeded in consolidating its recent gains and avoiding a potentially ruinous geopolitical overextension — holds any instructive insights for the early- to mid-twenty-first century United States.” Rehman holds that Tiberius was among Roman emperors one of the “most capable — at least with regard to the formulation of grand strategy and foreign policy.” George Santayana famously said that “those who cannot remember the past are condemned to repeat it.” Iskander Rehman and the applied historians would believe that one of the benefits of remembering the past is repeating what was most useful in it.

Whatever Tiberius’s deficiencies — his political ineptitude, his misanthropy leading on to paranoia, the tyranny of his last years — his foreign policy remained constant. He kept a steady eye — “a beady eye,” Rehman calls it — on the mismanagement of the men sent out to govern the provinces, and, in what was perhaps his one memorable remark, he instructed them all that the provinces, “like sheep, should be shorn, but not flayed.” He deliberately limited the expansion of the Roman Empire. “Over the course of his reign,” Rehman writes, “when presented with opportunities for peaceful annexation, Tiberius seems to have run careful cost-benefit analyses, and eschewed undifferentiated expansion.” What Rehman refers to as “the enduring loneliness of Tiberius’ genius” lay in his having recognized 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.”

On every occasion Tiberius plumped for consolidating over expanding the empire. Prudence was his hallmark. Yet, as Rehman notes, “prudent foreign policy, it would seem, does not make for entertaining history.” Something there is about Rome, in its years both as a republic and then as an empire, that excites comparison to the United States — and this much beyond Gibbon’s notion of decline and fall. I read Roman history for it, as well as for the glimmering light it throws on human nature generally. Ancient Greece for high culture, Rome for gritty reality.

Only late in his book does Rehman don the cloak of the applied historian. The final ten pages of Iron Imperator take up what America can learn from the reign of Tiberius. Many, of course, are the ways the two empires — if the United States ever precisely qualified as an empire — differ. For a prominent one, the United States, unlike Rome, has never known military defeat — not counting its two military stalemates in Korea and later Vietnam — whereas Rome under the triumvir Crassus lost roughly 20,000 troops and its leader in his abortive attack on Parthia, and later the Roman general Varus lost three Roman legions to Germanic tribes in the battle of the Teutoburg Forest. Owing to its isolated setting between the Atlantic and Pacific Oceans, the United States has never been invaded by foreign troops, while Rome had to fight off the incursions of Hannibal during the Punic Wars in the third century b.c.e.

But both Rome and the United States, each in its day, enjoyed world leadership. In both instances, this leadership did not go undisputed, Rome’s by Carthage and Parthia, the United States’ by first Nazi Germany and then the Soviet Union and now China, Vladimir Putin’s Russia, and Iran. Rehman writes:

By construing every regional crisis as a test of national will in a globe-girdling struggle with China, analysts in Washington also risk overly simplifying local conditions and disregarding the value and agency of small and mid-ranking powers. Last but not least, couching the U.S.-China relationship solely in terms of geopolitical enmity risks encouraging less wholesome and more nationally divisive sentiments.

Rehman goes on to ask how the U.S. should divide “its force levels in different theaters and tailor force planning constructs.” Here he refers to how the Romans successfully handled such conflicts. He feels that such strategic thinking as Tiberius employed “should be revived for the twenty-first century.” The argument is sophisticated and never less than interesting. History, one departs thinking, has lessons well worth not merely learning but putting into practice.

One cannot leave Iron Imperator without noting what a remarkable piece of bookmaking it is. Without a book jacket but instead with a copy of Lazzaro Baldi’s painting Saint Veronica Healing Tiberius with Her Veil on both its thick covers, handsomely illustrated throughout with lavish photographs of statues, busts, coins, drawings, and paintings, all elegantly laid out and printed on the highest-quality paper, Iron Imperator is a book that is a pleasure not only to hold but to behold.