Diodorus Siculus

Lore & Background

According to his own work, Diodorus was born in Agyrium in Sicily. With one exception, antiquity affords no further information about his life and doings beyond his written works. This visit was marked by his witnessing an angry mob demand the death of a Roman citizen who had accidentally killed a cat, an animal sacred to the ancient Egyptians. The latest contemporary event Diodorus mentions is Octavian's vengeance on the city of Tauromenium, whose refusal to help him led to Octavian's naval defeat nearby in 36 BC. Diodorus shows no awareness that Egypt became a Roman province—which transpired in 30 BC—so presumably he published his completed work before that event. Diodorus asserts that he undertook a number of dangerous journeys through Europe and Asia during his historical research and devoted thirty years to the composition of his history, suggesting his work was begun around the 70s BC.

Reader's Guide

Diodorus Siculus's significance lies in his ambitious attempt to create a universal history, the Bibliotheca Historica, which he arranged in three sections: the first six books are geographical in theme and describe the history and culture of Egypt (Book I), of Mesopotamia, India, Scythia, and Arabia (II), of North Africa (III), and of Greece and Europe (IV–VI). In the next ten books, he recounts human history starting with the Trojan War (Book VII) down to the death of Alexander the Great (XVII). The final section concerns the historical events from the successors of Alexander (Book XVIII) down to the time of the First Triumvirate of the late Roman Republic (XL). The end of the work has been lost, and it is unclear whether Diodorus actually reached the beginning of Caesar's Gallic War in 59 BC (as he promises at the beginning of the work) or, as evidence suggests, he stopped short at 60 BC owing to old age and weariness from his labors. His work is invaluable because it preserves fragments and summaries of earlier historians whose writings are otherwise lost, including Hecataeus of Abdera, Ctesias of Cnidus, Ephorus, Theopompus, Hieronymus of Cardia, Duris of Samos, Diyllus, Philistus, Timaeus, Polybius, and Posidonius. Only Books I–V and Books XI–XX remain in their entirety. The rest exists only in fragments preserved in Photius and in the Excerpta of Constantine Porphyrogenitus. One notable feature of Diodorus's writing is his tendency to provide unfulfilled cross-references, times where he includes notes similar to 'we will cover this matter later in the work' or 'see book X' but the topic is never addressed again in the surviving text. Catherine Rubicam suggests this is evidence of the author's change in temporal scope away from current events. In his preface, Diodorus writes that he will conclude with 'the beginning of the war between the Romans and the Celts' in 58 BC. Nevertheless, Diodorus even discusses Caesar's 55 BC incursion into Britain and his subsequent 44 BC deification.

Did You Know?

• Diodorus witnessed an angry mob in Egypt demand the death of a Roman citizen who had accidentally killed a cat, an animal sacred to the ancient Egyptians.
• The latest contemporary event Diodorus mentions is Octavian's vengeance on the city of Tauromenium in 36 BC.
• Diodorus asserts he devoted thirty years to the composition of his history, suggesting his work was begun around the 70s BC.
• Only Books I–V and Books XI–XX of the Bibliotheca Historica survive in their entirety; the rest exist only in fragments.
• Diodorus selected the name 'Library' as an acknowledgement that he was assembling a composite work drawing from many sources.

The Architecture of a Universal History

Diodorus conceived his Bibliotheca Historica as a sweeping panorama of human experience, organized into forty books across three distinct movements. The opening six volumes take a geographical approach, walking the reader through Egypt, the lands of Mesopotamia and India, the steppe peoples of Scythia, the deserts of Arabia, the coasts of North Africa, and finally the familiar terrain of Greece and Europe. The middle ten books pivot to narrative chronology, opening with the Trojan War and pressing forward through the age of Alexander the Great. The final twenty-two books carry the story from Alexander's successors all the way to the era of the First Triumvirate in the late Roman Republic. Each book begins with a table of contents and a reflective preface on the nature of history itself—passages scholars now attribute entirely to Diodorus's own hand. By Book X, he had adopted a strict annalistic framework, narrating every event across the known world year by year before advancing to the next. His ambition was nothing less than a single, unified account of the entire inhabited world and every period up to his own day.

A Mosaic of Voices

Diodorus chose the title "Library" deliberately, signaling to his readers that what they held was not a single original investigation but a carefully assembled composite drawn from a wide range of earlier writers. Among the authors he is known to have consulted are Hecataeus of Abdera, Ctesias of Cnidus, Ephorus, Theopompus, Hieronymus of Cardia, Duris of Samos, Diyllus, Philistus, Timaeus, Polybius, and Posidonius. In Book II, for instance, the Assyrian material is explicitly traced to Ctesias, while the description of India relies on Megasthenes and the fantastical "Islands of the Sun" come from Iambulus. Book I's treatment of Egypt draws heavily on Hecataeus of Abdera and Agatharchides of Cnidus. Yet the degree to which the narrative portions of the work are his own composition versus mere transcription remains a matter of ongoing scholarly debate. What is clear is that Diodorus saw himself as a curator of the historical record, stitching together the fragments of a vast literary tradition into a single accessible volume for his audience.

Thirty Years in the Making

The timeline of Diodorus's labor is reconstructed from clues scattered through his own text. He tells us he spent roughly thirty years composing the Bibliotheca, which would place the start of his work in the 70s BC. The earliest personal episode he records is his visit to Egypt during the 180th Olympiad, around 60 to 56 BC, where he witnessed a furious crowd demanding the execution of a Roman citizen who had accidentally killed a cat, an animal sacred in Egyptian religion. The latest contemporary event he mentions is Octavian's punitive action against the city of Tauromenium in 36 BC, whose refusal to assist him had contributed to a nearby naval defeat. Notably, Diodorus shows no awareness that Egypt had become a Roman province in 30 BC, suggesting he finished his work before that transformation. He also speaks of dangerous journeys across Europe and Asia undertaken in the service of his research. The precise endpoint of his narrative remains uncertain: he promised to reach the start of Caesar's Gallic War in 59 BC, yet the evidence points to a halt around 60 BC, possibly due to old age and exhaustion from decades of labor.

What the Ages Kept and What They Lost

The Bibliotheca Historica is, in its present form, a partial monument. Only Books I through V and Books XI through XX survive in their complete form; the remaining twenty-five books exist solely as fragments preserved in the writings of Photius and in the Excerpta compiled under Constantine Porphyrogenitus. Even within the surviving books, traces of the original's fuller scope are visible in the form of unfulfilled cross-references—passages where Diodorus promises to discuss a topic later in the work or directs the reader to a specific book, only for that promised material to be absent from the text we possess. The scholar Catherine Rubicam has suggested these dangling references may indicate that Diodorus shifted his temporal focus away from current events as he wrote. Books VI through X, which would have covered the transition from mythological to archaic history, are almost entirely gone. The result is a work that reads like a vast structure with entire wings missing, its surviving sections offering brilliant but incomplete glimpses of a once-unified narrative spanning the whole of the ancient world.

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