Defining the "most powerful" empire is a task that's bound to come with plenty of argument and about a million different suggestions. Should "powerful" focus on pure landmass? In that case, the title would go to the British, who once proudly proclaimed that the sun never set on their empire which, as Statista reports, once covered around 25 percent of the globe. Then again, it only lasted for a few centuries.

What about people? LiveScience reports that in the 5th century BCE, the Achaemenid Empire oversaw over 40 percent of the world's population. But it lasted only a little over two centuries, according to ThoughtCo. And while Imperial China has a stupendously long history spanning over two millennia, it experienced considerable ups and downs that greatly destabilized the empire, including the Mongol conquest of China in the 13th century (via National Geographic).

We need to find an empire that was around for a long time, enjoyed extended periods of stability, and had plenty of territory. Perhaps the strongest empire was one that could combine all of these, even if they weren't necessarily the highest-ranking in each category. That narrows things down considerably. So, what empire in history could have the expansionist policies and long-term wellbeing that fit the bill, perhaps with some colorful history thrown in as well? For that, we should turn to ancient Rome.

Most historians generally agree that the Roman Empire began in 27 BCE. According to History, that's when Octavian, who had previously defeated Marc Antony and Cleopatra in 31 BCE, became Emperor Augustus. Though one might argue that his predecessor, Julius Caesar, ruled quite like a singularly powerful emperor, it was Augustus who took the official title and heralded the transition of the Republic into an Empire.

The matter of when Rome ended, however, is a bit trickier. Some might argue that the end of the empire proper came during the reign of Diocletian in the late 3rd and early 4th centuries CE, when he split the unwieldy empire into western and eastern halves. Each half was governed by two rulers.

While Western Rome fell in 476 CE, says How Stuff Works, the eastern half did quite a bit better. It eventually morphed into the Byzantine Empire, which then lasted until the Ottomans took over Constantinople in 1453 CE. Going by that metric, the Roman Empire was around in one form or another for well over a millennium. And, while it didn't have the landmass of the British Empire at its height or the relative population of the Persian Achaemenid Empire, Imperial Rome was generally longer-lasting and more stable than practically any other historic empire. When it comes to power, permanence and stability — especially when they last for centuries at a time — count for quite a lot in the empire game.

Over much of its history, one of Imperial Rome's greatest glories was its military. Simply put, there was nothing like it in the world. With its mighty army, Rome was able to expand its borders, bring in new citizens, and establish its historical reputation.

What made Roman forces so great? For one, during the time of the Roman Empire, they were recruited for years-long terms, says the Ancient History Encyclopedia. This contrasted with the earlier military model used during the Republic, when groups of soldiers disbanded after a conflict. Soldiers had to meet certain standards of fitness and could be sent far afield in service of the empire, but they were granted landholdings at the end of the term. Overall, it was a harsh existence, but it at least offered a kind of stability, especially in terms of food and money, that wasn't guaranteed to every Roman, citizen or otherwise.

The Roman Army was also very disciplined, as the BBC reports. Soldiers could be expected to march up to 20 miles per day when they weren't busy fighting or endlessly training. That training paid off, though, as battlefield tactics could make or break a fight. They also had the advantage of weaponry, from swords, to projectiles, to horse-mounted cavalry forces that oftentimes overwhelmed their opponents.

Investment in the military turned out to be a pretty profitable enterprise for Imperial Rome. Per Britannica, the 2nd century saw increased Roman military expansion into foreign territories. This meant plenty of war with different non-Romans along the way, but more often than not, that Roman military machine prevailed. And, when it did, the Empire sent citizens abroad to establish colonies in places as far afield as modern-day Spain and Britain.

The Romans themselves were often cited as saying that they only fought wars when provoked, but the trail of profit that follows behind their military victories is suspicious. Expanding the empire opened up access to economic advantages, though sources from the time period also point to cultural drives as well, like proving the worth of yourself and your people on the battlefield.

But this expansion eventually came with a price. When the Empire extended Roman citizenship to all free people in 212 CE, as History reports, things got difficult. The vast array of territories grew unwieldy and difficult to manage in a world where instantaneous communication was a wild dream.

As much as Imperial Rome seemed set on making war or, perhaps in their words, bringing Rome to non-Romans, life within the Empire actually wasn't so bad. For over a century, Rome was able to manage a period of peacetime that was so extended we're still talking about it over a millennia later. Called the "Pax Romana," this period of peace lasted from about 27 BCE to 180 CE, according to ThoughtCo. The actual phrase, however, comes courtesy of 18th century historian Edward Gibbon, who debuted the concept in The History of the Decline and Fall of the Roman Empire.

The relative peace within the empire allowed many to achieve new cultural and technological advancements that would have been difficult under more strenuous times. Romans also benefited from tax reform, says the Ancient History Encyclopedia, which may not sound immediately exciting but did free up resources for the city of Rome in particular. Emperor Augustus, who kicked off the new tax system, also rebuilt temples, shored up supplies in case of disaster, and strengthened the ancient city's police force.

Yet, there were occasional hiccups during this period, like the reign of Nero, and those foreign people who weren't too happy about Roman expansion into their territories. Still, compared to the kind of upset that roiled Rome at other times, this was a uniquely steady period in the history of the empire.

At first glance, you might think that being the Emperor of Rome was a pretty plum job. Sure, you might need to attend a meeting or two, maybe preside over a battle every once in a while, but the rest of the time you're lounging about being fed grapes and listening to someone playing the lyre, right? The truth is, while Roman emperors enjoyed plenty of power, theirs was also a position full of paranoia and deadly political intrigue, according to PBS. After all, that talented lyre player might also be an assassin sent by your political enemies. And are those grapes poisoned?

Emperors were supposed to rule for life, meaning that anyone who was deemed unfit for the role — whether they were mentally ill, overly powerful, or just simply unpopular — might meet an untimely end. Even if they didn't die via poison or stabbing, emperors still had to sacrifice much in the name of power, whether it was divorcing a beloved spouse or killing one's own troublesome family members, just to stay on top.

According to the Ancient History Encyclopedia, all of those imperial dynasties could get dangerously tangled. Only four of the first 12 Roman Emperors appear to have died of natural causes. Six would meet their ends through murder or assassination, while two even brought their own lives to an end, proving that the Imperial throne was hardly any protection after all.

Much like the military, the intensity with which Rome invested in technology has been credited as one of its keys to success. Though some technologies debuted when Rome was still a republic, these advances were refined and still very much in use by the time the Empire came around.

So what, exactly, were the sorts of technological advances that made Imperial Rome such a big deal? According to History, these included the refinement of the (for them) ancient concept of aqueducts, which first came about in the 3rd century BCE and allowed cities to pop up far from water sources. And those marching men in the famous Roman military would have had an even tougher time of things if they didn't sometimes get to use paved Roman roads, which also proved useful for traders, immigrants, and all other sorts of travelers. By the time of the empire, regular folks could also read newspapers and would even eventually have potential access to bound books.

The military was also supported by considerable advances in battlefield medicine, according to the St. Louis Science Center. While Roman medical care still doesn't compare to modern technologies and anesthetics, it was still a far sight better than in other times and places. Ancient surgeons advanced the use of tourniquets to stanch bleeding, started doing basic preventative care like physicals, and even made some of the first steps to sanitize the notoriously dirty world of the battlefield.

Imperial Rome, like so many other societies, operated on a highly structured and hierarchical system. As PBS says, the emperors were clearly at the top of the pecking order. They were followed by high-class Patricians, then the Equites, second-class Plebeians, freedmen, and, finally, slaves. Those stratifications were clearly delineated by social circles, finances, clothing (the emperor was the only one who was supposed to wear a purple toga), and laws.

Traditionally, it was incredibly tough to move between social classes, meaning that social climbers throughout much of Rome's history would have been very frustrated indeed. Yet, the rise of the empire meant that some of those structures began to soften. A patronage system opened up routes to power for some, while others simply leveraged loads of money. Eventually, Emperor Augustus opened up the Equites class to more people and allowed them to take seats in the vaunted Roman Senate.

But as the Ancient History Encyclopedia points out, that system only really applied to a select group of men. Women were typically expected to remain in the home under the authority of a father or husband, though, as in many societies, lower-class women were obliged to work while upper-class ones sometimes got involved in politics and religion, like the Vestal Virgins. Slaves, meanwhile, were solidly at the bottom of society. Quite a few were captured foreigners, unwillingly contributing to the economic growth of the empire far from their own homes.

At its height in roughly 117 CE, Vox reports, the Empire had control of Britain to the north and Egypt to the south. The Romans would eventually expand west to the Atlantic Coasts of Europe and what's now Morocco and as far east as Babylon (in modern day Iraq) and Armenia. Though, it's important to note that this wasn't the largest-ever mass of land controlled by a single empire. That distinction would go to the British Empire, which Statista reports controlled nearly a quarter of the world's land by 1920. Yet, especially in terms of the ancient world, the sheer amount of land and number of people under Roman control was still utterly staggering.

Foreign policy became critically important as the frontier became a political as well as a military realm. According to Khan Academy, the early Empire focused on military expansion, while later forces were more intent on holding the line and maintaining borders. Slowly but surely, Roman influence was felt more in the political sphere of these borderlands than in its fighting force.

Roman emperors have a pretty bad rap. For some of them, that reputation is probably somewhat deserved, though the true stories of notoriously naughty rulers like Nero and Caligula are perhaps more complicated than you might realize. Yet, for others, it's not really fair to lump them in with an emperor whom legend says made his horse a Roman politician. Some of them might even rightfully be called "good."

At least, that's their reputation. The "Five Good Emperors," as described by the Ancient History Encyclopedia, were, well, five Roman emperors who managed to leave the realm looking a little better than how they found it. Those five also, maybe not coincidentally, reigned in succession. It began with Nerva in 96 CE, who was followed by Trajan, Hadrian, Antoninus Pius, and finally Marcus Aurelius, whose rule ended in 180 CE.

What made them so good? According to Britannica, the Five Good Emperors presided over a truly grand expansion of the Roman Empire. The system of government ran relatively smoothly and practically everyone whose territory was conquered by Roman forces went along and became pretty Romanized themselves. It wasn't all perfect, though, as this is the era in which the emperor started to become something of a dictator and previously independent institutions like the Senate became filled with his cronies.

Sometimes, success comes back to haunt you. In the case of Imperial Rome, all of the military might, cultural expansion, and new territories started to become downright unwieldy. That's why, around 285 CE, Emperor Diocletian split the empire into Eastern and Western halves, according to ThoughtCo. The new system was referred to as a "tetrarchy" that encompassed four different rulers, also known as a "rule of four." Basically, each half would have a primary ruler with a subordinate ruler acting as a sort of vice president (but with more power), called a "caesar." Diocletian would continue to rule in the east, while his counterpart in the west was Maximian. 

But why would Diocletian give up so much of his power in this dramatic change? The empire had simply grown so vast that it was incredibly difficult to govern it effectively from Rome. As Vox reports, travel and therefore communication in the Roman world could be excruciatingly slow. It was also an empire wracked with crises. By the third century, it was painfully clear that an emperor could be assassinated, leaving behind a potentially deadly power vacuum. It's very likely that Diocletian wanted to make it almost impossible to topple the Empire by killing a single ruler, as there would have been three more to take his place.

As the Roman Empire moved on, its relationship to religion became increasingly tangled. Originally, pretty much everyone in Rome could be considered a "pagan," though Pagans: The End of Traditional Religion and the Rise of Christianity argues that they wouldn't have called themselves as such. They just would have worshipped the gods like everyone else, even if those deities had different names elsewhere and the Romans were often riffing on Greek traditions.

Then, Christianity happened. While it's true that early Christians did experience persecution in the Roman Empire, the BBC reports that things softened as time went on. Eastern Roman Emperor Constantine the Great even converted to Christianity sometime in the 4th century and officially accepted it in the Edict of Milan. A decade later, it was the state religion.

However, some wonder if Constantine had non-spiritual reasons for his conversion. Some accounts say that he didn't formally convert until he was on his deathbed. Other legends maintain that he converted after a vision pushed him to fight a battle under the Christian symbol of the cross, as ThoughtCo reports. Or maybe Constantine had a guilty conscience for committing the sorts of crimes emperors tended to commit and wanted absolution. Perhaps he rightfully predicted that Christianity would become a major cultural and political force and jumped on the train early. Whatever the motivation, Constantine's reforms almost certainly helped pave the way for the emerging religion.

Though it sounds like a dramatic, singular event, the truth is that the "fall of Rome" is actually pretty tough to pin down. How exactly can you pick out the "end" of a civilization that existed for so long, in part because it was often ideologically flexible? Did Imperial Rome end when Diocletian basically threw up his hands and cut the empire in two? Did it become something totally different and not-Rome when Constantine gave Christians the thumbs up?

According to ThoughtCo, 18th century historian Edward Gibbon picked 476 CE, when Western Rome fell to barbarian invaders led by Odoacer, who deposed the last western emperor, Romulus Augustulus. That was admittedly pretty dramatic, assuming Odoacer knew how to make an entrance. But, then again, Eastern Rome was still around, eventually transforming into the Byzantine Empire.

If you accept that "Rome" was still holding on in Byzantium, then the empire was still around by the time Constantinople was taken by the forces of the Ottoman Empire in 1453 CE. So, when Rome fell all depends on who you ask. Ultimately, there isn't a single, dramatic event that we can point to, meaning that historians have plenty to argue about many centuries after the fact. Even then, many would likely agree that Rome, whatever it was, still remains the strongest empire in human history.

Being Roman emperor was one of the most demanding and dangerous jobs in history. Sure, the compensation was pretty good—having the entire Roman Empire at your disposal was pretty lucrative—but it was also really, really dangerous. Very few Emperors died peacefully in their sleep, if you catch our drift.

That didn't dissuade people from competing for the throne, however. Since the imperial succession wasn't really hereditary, anyone with the right combination of influence, military power, and money could potentially be emperor (and one guy, Didius Julianus, literally just bought the throne from the Praetorian Guard). That means that some of the most ambitious people in history schemed to gain the imperial purple.

Not all of them succeeded, because ambition, money, and power weren't the only requirements for the job—you had to be extremely devious as well. Only those who could play politics and who were willing to do anything and betray anyone could become the most powerful individual in the ancient world. But once in power, even the most devious Roman emperors in history found out that winning the throne was only half the battle. The hard part was staying alive long enough to enjoy it.

Rome's first emperor by modern reckoning was also one of its most devious. Born Gaius Octavius (and often called Octavian), as the Encyclopedia Britannica notes Julius Caesar was his great-uncle on his mother's side, and Caesar pushed Octavian's career throughout his life. When Caesar was assassinated, his will formally adopted Octavian as his son and heir, and he became Gaius Julius Caesar Octavianus.

Caesar's death sparked a civil war. Octavian was just 18-years-old, but he decided to claim his inheritance as Caesar's heir, pitting him against Caesar's right-hand man, Mark Antony. Octavian now had Caesar's immense wealth, and his adoption made him popular with Caesar's old troops. More importantly, as History Extra reports, the Roman Senate viewed Octavian as no threat, so they supported him, assuming they could manipulate him.

As it turned out, Octavian was manipulating everybody. He formed a triumvirate with Antony and a general named Lepidus—and bided his time. When Antony gave him an excuse by marrying the Egyptian queen Cleopatra, Octavian pounced, defeating his enemies and assuming all power in Rome. Octavian knew the Roman people would reject a king, so he insisted the only honor he would accept was "princeps," or "first citizen." He made a big show of returning authority to the Senate, then slowly claimed power behind the scenes. He was emperor before anyone even had a word for the office, and single-handedly reshaped Rome into his personal empire.

Caligula was the third emperor of Rome, and he was a disaster, remembered today mainly for his insanity—he talked to the moon, declared war on the ocean, and wanted to make his horse a consul. Except, as History points out, most of that is probably not true. While he was definitely crazy and a terrible emperor, Roman historians had a bad habit of exaggerating things or inventing stuff completely in order to make reviled figures like Caligula look worse. The tragedy is, he started off as one of the most devious Roman emperors before suddenly veering into crazy.

First of all, he survived a political purge that killed most of his family, then ingratiated himself with the aging emperor Tiberius, who named him and his cousin Gemellus co-heirs. When Tiberius died, Caligula forged an alliance with Naevius Sutorius Macro, the leader of the Praetorian Guard, and pushed Gemellus aside. Then, a year later, he had them both killed.

For the first few months of his reign, Caligula cunningly courted public opinion. He spent lavishly on public works, he was respectful of traditions, and he announced a general amnesty for everyone who'd fled Tiberius' paranoid purges. But as one historian notes, Caligula probably suffered from temporal lobe epilepsy—a disease that likely pushed him into mental instability. The rest of his reign was chaotic, violent, and so deeply unpopular he was the first emperor to be assassinated for the good of the empire.

When Tiberius Claudius Drusus was born in 10 B.C., no one thought he might someday be Emperor of Rome. Although he was related to the first two emperors, he was also a weak and sickly boy. He stuttered, had tremors, and his nose ran constantly. According to History, theories on what exactly afflicted Claudius range from cerebral palsy to Tourette's syndrome. Whatever the truth was, his own family found him embarrassing.

When his nephew Caligula was assassinated, there was chaos in Rome. The Praetorian Guard were in a bit of a bind; since they'd done the assassinating, they worried that whoever claimed the throne would take revenge on them, so when they found old Claudius—already 51-years-old and widely considered a fool—hiding in the palace, they proclaimed him emperor, assuming he'd be a friendly and easy-to-control figurehead.

Claudius promptly proved how devious he actually was. First, he paid off the Praetorian Guard with a huge amount of money, knowing full well he owed his position—and his safety—to them. He skillfully avoided appearing before the Senate until he had consolidated his position. His ailments suddenly became much less pronounced. And then, as the Encyclopedia Britannica explains, he went on to be one of Rome's better emperors. In fact, it's widely believed that Claudius leaned in to his reputation as a fool and played up his symptoms in order to survive, and his little act paid off handsomely.

Nero Claudius Caesar Augustus Germanicus was the great-grandson of Rome's first emperor, Augustus. Under Emperor Caligula he and his mother Agrippina were exiled, but after Caligula's assassination and the ascension of his uncle, Claudius, to the throne they returned to Rome. Agrippina married Claudius, Claudius adopted Nero, and not long after Claudius died under mysterious circumstances (funny how that happens).

As the Encyclopedia Britannica notes, Nero was just 16-years-old when he was proclaimed emperor, and he ruled for 14 years. He quickly gained a reputation for outlandish appetites and huge ambitions, but what most people remember about Nero is that he's the emperor who fiddled while Rome burned. 

Rome did indeed burn—as The Washington Post notes, 10 of Rome's 14 districts were totally destroyed in the fire—but there was no fiddling. Nero's response to the disaster was suspiciously nonchalant, however, possibly because he'd set the fire deliberately in order to build an enormous palace for himself. As PBS reports, Nero's desire to tear down most of the city and build his "Neropolis" was no secret—but the Senate wouldn't approve the plans. Many historians believe that Nero deviously destroyed his own capital in order to get what he wanted.

The late 1^st century wasn't a great time for Rome. People had figured out that there was a formula for seizing power in the empire—have a lot of money and a lot of troops. Emperor Commodus was assassinated at the very end of the year 192, sending the empire spiraling into chaos. The next year became known as The Year of the Five Emperors because ... there were five emperors that year.

Pertinax was acclaimed emperor but forgot who got him there and refused to pay the Praetorian Guard a huge bribe, so they killed him too. The Guard then auctioned the throne to the highest bidder, won by Didius Julianus, who made it nine weeks before being killed in turn.

Through it all, as the Encyclopedia Britannica records, Septimius Severus kept his head down. As a former Consul and current governor of Upper Pannonia (located in modern Austria and Hungary)—not to mention having one of the biggest armies behind him—he was perfectly positioned to claim power. But he waited until the right moment. First, he made a deal with his chief rival, Clodius Albinus, which freed him to march on Rome. Once installed as emperor, Severus replaced the Praetorian Guard with his own bodyguard. Then, according to The Collector, he quickly betrayed Albinus and marched his armies against him. When the dust settled, Severus had established a new dynasty and reshaped Rome into a military monarchy.

Septimius' son, Caracalla, is remembered as a terrible emperor who contributed significantly to the decline of the empire. His actions are considered to have contributed directly to what historians flatly call The Crisis of the Third Century. Even the Encyclopedia Britannica casts significant shade on him, calling him "a bloodthirsty tyrant."

Named co-heir with his younger brother, Geta, Caracalla became the senior emperor when their father died in 211. As one historian writes, the brothers had been rivals their entire lives, and Caracalla showed his devious side when he lured Geta to their mother's house and had him murdered. Caracalla then raced to the Praetorian Guard and claimed he'd been attacked—and killed Geta in self-defense.

Caracalla was a bad administrator, and he sought to gain popularity by throwing lavish entertainments for the citizens. These were expensive, however—as was the army, which he needed on his side. In 212, Caracalla made history by decreeing all free people inside the empire's borders would be citizens of Rome. This was monumental, as Roman citizenship had a lot of perks in the ancient world and had been used as a reward for centuries. But as one biography explains, Caracalla was being calculating: Not only did custom dictate that all new citizens adopt the name of their sponsor—meaning that millions of new citizens now added "Antonius" to their names—but this act of seeming benevolence increased the tax revenue significantly.

In the early 3^rd century, the Praetorian Guard—essentially the emperor's bodyguard and private security force—had become incredibly powerful. Emperors were frequently chosen by the Guard—and just as frequently assassinated by the Guard.

Caracalla was a cruel and unpredictable emperor, and was paranoid. He often executed people simply because he suspected them of plotting against him. A man named Macrinus was a prefect of the Praetorian guard under Caracalla, and gained the trust of the emperor. Macrinus was a talented man, but he was not of Senatorial rank, and so under normal circumstances would have no hope of becoming emperor. However, according to History Extra, when Macrinus accompanied Caracalla to battle in what is modern-day Iran, he was alarmed when a prophecy began to circulate that he would depose Caracalla and become emperor—he knew Caracalla had executed people for less. As the Encyclopedia Britannica reports, Macrinus thought quickly, recruiting an army officer to assassinate Caracalla before the emperor could order his execution.

Macrinus was acclaimed emperor—the first Praetorian to achieve the rank. He tried to be a good emperor, actually, but he made the classic mistake of trying to reduce payments to the army. A little over a year into his reign, he was deposed, captured, and executed.

If Augustus created the Roman Empire, Diocletian saved it—for a while. Crafty and cunning, Diocletian rose up from an obscure and low-ranking background to become a military leader during the period of Roman history called The Crisis of the Third Century. This period was marked by chaos, as emperors were assassinated and the army promoted replacements regularly.

When Diocletian was proclaimed emperor in 284, he moved like a man with a plan. First, according to the Encyclopedia Britannica, he promptly accused the father-in-law of the previous co-emperor—who had, of course, been murdered—of committing the crime, and had the man executed to stop rumors it had actually be Diocletian's doing. Then, after fighting off several rivals, Diocletian was sole emperor—but he was smart enough to realize the empire was simply too large for one man to run. As Money Museum writes, Diocletian divided the empire into East and West and made a trusted colleague named Maximinianus his co-emperor. Then he elevated two more men to a new rank called Caesar.

But if you need more proof of Diocletian's devious nature, consider this: As one historian notes, Diocletian is the only Roman emperor to simply retire. In 305, he gave up the purple—and forced his colleague Maximian to retire as well. Diocletian died peacefully in his bed a few years later—a remarkable testament to his ability, considering that 62 percent of Roman emperors died violently.

Constantine I, known as the Great, was the first Roman Emperor to convert to Christianity. As the Encyclopedia Britannica explains, he claimed he saw a vision on the eve of a battle with his rival Maxentius that instructed him to paint a Christian symbol on his troops' shields. After winning the battle and going on to be sole emperor, he publicly ascribed his success to his conversion.

Many historians think Constantine was being a bit craftier than the legend implies. After centuries of violent suppression, Christianity was rising in popularity in Rome. As one biography explains, Constantine used the trappings of Christianity to imbue his court with a religious and mysterious aura, and used the growing popularity of the religion in service of stabilizing the empire and his control of it.

Constantine was actually very slow and careful to push out the old pagan religions, which were still very popular, especially among the troops. He only gradually removed pagan symbols from official documents, and closed down temples in stages. He was cunning about remaking the empire in a Christian image that saw him as the most important member of the church—although an unofficial member, since he delayed baptism until he was on his deathbed, possibly in an example of the ultimate hedging of bets.

The later Byzantine emperors are generally less famous than their earlier counterparts. Although the Byzantine Empire is considered a successor state to the classic Roman Empire, the Byzantines considered themselves Roman. And there's a reason we use the term "Byzantine" to describe something especially complex—they were a devious bunch.

According to Rearview Mirror, Leo III worked hard to become emperor in 717. He wasn't part of the ruling class, he was a soldier, but he double-crossed and schemed his way into a leadership position. His double dealing wasn't restricted to his career—the empire was under tremendous pressure from invading Arab forces at the time. As the Encyclopedia Britannica writes, Leo made a deal with Arab leaders, agreeing to be their vassal if they helped him gain the throne. With their support, he marched on Constantinople. Then, when Emperor Theodosius III didn't seem inclined to die on his own or step aside, Leo cooked up a plot to kidnap Theodosius' son to force him out. And it worked.

Leo III also gets credit for saving the empire from the Arabs. After defending the city from overwhelming odds, he proved to be such a clever negotiator he was able to reorganize the empire, strengthening it and ensuring its survival for centuries to come.

In the 13^th century, the Byzantine Empire was ailing, but was seen as the most important Christian empire standing against Muslim forces. As Encyclopedia Britannica explains, Byzantine emperor Isaac II had been deposed some years earlier, so his son encouraged the Pope to declare a Fourth Crusade in order to restore his family to power. It worked, but it also meant that Isaac and Alexios were bound to the Crusaders, and the people of Constantinople came to despise these foreign invaders. The Crusaders believed they were owed by Isaac for their help, and when he couldn't pay they simply took what they could from the city, setting fires and looting.

Enter Alexios V Doukas, nick-named Murtzuphlus. Smelling an opportunity, Doukas harnessed the anger of the crowd in order to inspire a full-fledged revolt against Isaac and his son, leading a mob against the palace. As The Fourth Crusade records, the Emperors barricaded themselves inside their chambers. Doukas put his devious mind to work. With the help of someone with access to the imperial treasury, he bribed the emperors' bodyguards, the Varangian Guard, and had the co-emperors arrested and eventually killed, declaring himself the new emperor.

That's where Doukas' luck ran out. He discovered the empire was broke, so he decided their debt to the Crusaders was illegitimate. They laid siege to the city, and four months later Doukas—and the Byzantine Empire—fell.

Constantine was the last Byzantine Emperor—the man who literally watched Constantinople fall to the Ottoman Empire in 1453, so naming him one of the most devious Roman Emperors might seem a stretch. But his failure was almost guaranteed by the time he ascended to the throne.

As Rearview Mirror records, Constantine was forced to stand by and watch as his incompetent brother, John VIII, ruined what was left of the declining empire. The Encyclopedia Britannica notes John had tried to enlist the help of the Western powers by going to Italy and joining the Eastern Orthodox Church with the Catholic Church under the leadership of the Pope—but his people were enraged by this, and it produced no significant help. Broken, John died shortly afterward, and Constantine ascended to the throne.

He tried. With no money, a small, sloppy army, and no allies, Constantine held on for five years and proved to be very tricky. As The Immortal Emperor notes, he tried every possible diplomatic trick to keep his empire together, but with little success. But the fact that he kept things going as long as he did is a testament to his cleverness. And the fact that he was last seen leading a suicide charge against Ottoman forces in Constantinople is a testament to his bravery.