The 500 years of the Roman Empire (27 B.C. to A.D. 476) gave history some of its most noteworthy—and most diabolical—leaders. The major emperors are names that are familiar to most every student of Western civilization: Augustus, Tiberius, Caligula, Claudius, Nero, Trajan, Marcus Aurelius, Diocletian, and Constantine I (called “the Great”).

Augustus, Tiberius, Caligula, Claudius, and Nero were the first five emperors, a succession covering 75 years of Roman rule. Octavian (63 B.C.–A.D. 14), later known as Augustus, became Roman emperor when, after the assassination of his great-uncle, Julius Caesar, a power struggle ensued and he defeated Mark Antony and Cleopatra to take the throne. Under Augustus’s rule from 27 B.C. to A.D. 14 began the 200 years of the Pax Romana, a period of relative peace. During this time no power emerged that was strong enough to sustain conflict with the Roman army. Consequently, Rome was able to turn its attention to the arts, literature, education, and trade.

As second emperor of Rome, Tiberius (42 B.C.-A.D. 37) came under the influence of Roman politician and conspirator Sejanus (d. A.D. 31). Tiberius was the adopted son of Emperor Augustus, and though he had been carefully schooled and groomed to take on the leadership role, ultimately he became a tyrannical ruler; the final years of his reign were marked by viciousness and cruelty. Upon Tiberius’s death, his nephew Caligula (A.D. 12–41) ascended the throne. Born Gaius Caesar, he was nicknamed Caligula, meaning “Little Boots,” since he was brought up in military camps and at an early age had been dressed as a soldier. For a short time Caligula ruled with moderation. But not long after he came to power, he fell ill and thereafter exhibited the erratic behavior for which he is well known. Most scholars agree that Caligula must have been crazy. He was murdered in A.D. 41, and Claudius, also nephew to Tiberius, was then proclaimed emperor.

Claudius (10 B.C.-A.D. 54) renewed the expansion of Rome, waging battle with Germany, Syria, and Mauritania (present-day Algeria and Morocco), and conquering half of Britain. Though his administration was reportedly well run, he had his enemies; among them was his niece, Agrippina the Younger (A.D. 15?-59), who is believed to have murdered him in 54, after securing her son, Nero, as successor to the throne.

In Nero (A.D. 37–68) the early Roman Empire had perhaps its most despotic ruler: Though his early years in power were marked by the efficient conduct of public affairs, in 59 he had his mother assassinated (she reportedly had tried to rule through her son), and Nero’s legacy from that point forward is one of ruthless behavior. He was involved in murder plots, ordered the deaths of many Romans, instituted the persecution of Christians, and led an extravagant lifestyle that emptied the public coffers. He was declared a public enemy by the Roman Senate and in the year 68 took his own life.

With the exception of Augustus, the first century A.D. of the Roman Empire was marked by extreme rulers. The second century A.D. was marked by the leadership of soldiers and statesmen. Trajan (53–117), who ruled from the year 98 until his death 19 years later, is best known for his military campaigns, which expanded Rome’s territory. He was also a builder—constructing bridges, roads, and many buildings. When Marcus Aurelius (121–80) ascended to emperor in 161, he had already been in public office for more than 20 years. A man of great experience, he was reportedly both learned and of gentle character. His generals put down revolting tribes, and, in addition to winning victories along the Danube River, his troops also fought barbarians in the north. Diocletian (245?-313?) had served as an army commander before becoming emperor in 284. In an effort to effectively rule the expansive territory, he divided it into four regions, each with its own ruler, though he himself remained the acknowledged chief. Two years before he abdicated the throne (305), he began the persecution of Christians—a surprising move since he had long been friendly toward them. Unlike his predecessors who died in office, Diocletian had a retirement, which he reportedly spent gardening.

Constantine the Great (who ruled from 306 until his death in 337) is notable for reuniting the regions that Diocletian had created, bringing them all under his rule by 324. He was also the first Roman emperor to convert to Christianity. Theodosius I (347–395), also called “the Great,” is known to many since he was the last to rule the united Roman Empire (379–95).