What Are the Principal Sources of Emperor Caligula’s Reign?

To many, Emperor Caligula was one of the most infamous Roman rulers. However, almost all we know about Caligula’s controversial reign comes from sources biased towards the emperor.

Mar 11, 2024By Vedran Bileta, MA in Late Antique, Byzantine, and Early Modern History, BA in History
sources of emperor caligula reign


Gaius Caesar Augustus Germanicus, better known as Caligula, was the third emperor of the Julio-Claudian dynasty. Yet, despite the illustrious origins, going back to Emperor Augustus and Julius Caesar, Caligula is notorious for his alleged madness, tyranny, cruelty, megalomania, and salacious stories involving intimate relationships with his sisters. In short, Caligula is the poster boy for crazy Roman emperors.


However, we must be aware that most of our information about Caligula’s turbulent and controversial reign comes from just a few sources. Namely, Suetonius and Cassius Dio, who both lived decades after Caligula’s violent death and were eager to record the emperor’s worst scandals, excesses, and maniacal behavior to further their agenda. Thus, we should be careful when reading those sources and be able to set them in a historical context, separating fact from fiction. 


The Man Who Made Caligula a Madman: Suetonius

caligula famous horse statue
Statue of a youth on horseback (probably representing emperor Caligula), early 1st century CE. Source: The British Museum, London

The most important but controversial source for Caligula’s reign was not a historian but a biographer. Gaius Suetonius Tranquillus, or simply – Suetonius – wrote The Twelve Caesars, a seminal biography of the first twelve Roman emperors, including Julius Caesar. However, despite having access to the imperial archives, Suetonius decided to fill his work with as much gossip, anecdotes and rumors as possible. He focused on the lives and characters of the emperors rather than their political and military achievements.


Suetonius’ Caligula is a depraved and insane tyrant who committed countless atrocities and acts of madness, including the infamous tale of Incitatus, the horse that Caligula wanted to make a consul (this never happened). Suetonius enjoyed describing salacious stories, such as Caligula’s very close relationship with his younger sisters and their public displays of affection.


However, we should be aware that Suetonius not only lived decades after emperor Caligula’s demise. Suetonius was also a senator and was hostile to Caligula, an absolutist ruler who spent most of his reign in conflict with the Senate. In addition, Suetonius was a personal friend of emperor Hadrian. Thus, by vilifying the Julio-Claudian emperors, Suetonius strengthened the legitimacy of the later imperial dynasties.

Caligula’s Reign as a Moral Story: Cassius Dio

praetorian guard
Relief depicting the Praetorian Guard (originally part of the Arch of Claudius), 51-52 CE, Louvre-Lens, Lens

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Like Suetonius, Cassius Dio was a Roman senator. He was also a historian and author of a comprehensive history of Rome from its foundation to his own time. Part of the Roman History, Book 59, is dedicated to Emperor Caligula’s reign. Cassius Dio was an ardent supporter of the imperial system. Yet, he was also critical of the vices of the incapable emperors, who threatened the Roman Empire’s stability and security. Emperor Caligula was one of these incompetent rulers, a monstrous and irrational emperor who abused his power and offended the gods. Thus, for Cassius Dio, the ultimate proof of Caligula’s abuse of power was the emperor’s demand to be worshipped as the living god, which ultimately led to his death at the hands of the Praetorian Guard.


Cassius Dio’s account, however, is not entirely negative. He acknowledged some of Caligula’s positive qualities and achievements, such as the emperor’s popularity at the onset of his reign. He also provided details regarding Caligula’s political and military acts, such as the attempt to invade Britain or his annexation of Mauretania. For Cassius Dio, who lived in the mid-second century, Caligula’s vices also serve to praise the virtues and reforms of his contemporaries, the emperors of the Severan dynasty.


Caligula as a Complex Emperor: Flavius Josephus and Philo of Alexandria

caligula cuirass bust
Cuirass bust of the emperor Caligula, 37-41 CE, Ny Carlsberg Glyptotek, Copenhagen


Suetonius’ account of Caligula contains valuable material, but much of it is biased and exaggerated. The account of Dio Cassius survives only in summaries and extracts, while Tacitus’ books on Caligula are lost, leaving us only with the account of the emperor’s father Germanicus. Thus, to fill the gaps, we rely on two minor sources. The first one is Flavius Josephus, a Jewish historian and apologist, who is best known for his “Jewish War” and “Antiquities of the Jews,” both dealing with the history of the Jews and their relationship with the Romans. Josephus, who was born a few years after Caligula’s death, also left us a valuable record of Caligula’s death, of the assassination plot and its aftermath.


alma tadema death caligula painting
A Roman Emperor: 41 CE, (depiction of Claudius), by Sir Lawrence Alma-Tadema, 1871. Source: The Walters Art Museum, Baltimore


Philo of Alexandria was not a historian but a Hellenistic Jewish philosopher. However, he is the only source who is a contemporary of Caligula and was able to meet the emperor. Philo was part of a Jewish delegation that went to Rome in 38 CE to appeal to the emperor to stop the persecution and discrimination of the Jews in Alexandria. This visit is described in detail in Embassy to Gaius and Against Flaccus. Philo criticized Caligula for his blasphemous acts, such as the emperor’s plan to erect a statue of himself in the Second Temple in Jerusalem. However, Philo also participated in one of the emperor’s infamous banquets. Interestingly, he noticed nothing similar to Suetonius’ scandalous incidents. Thus, Philo’s accounts are among a few rare sources presenting Emperor Caligula as a complex but flawed historical figure.  

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By Vedran BiletaMA in Late Antique, Byzantine, and Early Modern History, BA in HistoryVedran is a doctoral researcher, based in Budapest. His main interest is Ancient History, in particular the Late Roman period. When not spending time with the military elites of the Late Roman West, he is sharing his passion for history with those willing to listen. In his free time, Vedran is wargaming and discussing Star Trek.