Alexander the Great: The texts of Plutarch and Diodorus

What happened

Alexander the Great remains one of the most recognizable figures in human history, yet the contemporary records of his life and conquests have entirely vanished. The generals, philosophers, and historians who traveled with him across the Persian Empire wrote extensive accounts, but none of these original texts survive today. Instead, modern understanding of the Macedonian king relies heavily on writers who lived centuries after his death. Two of the most significant surviving accounts are Plutarch’s Life of Alexander and Book XVII of Diodorus Siculus’s Library of History. These two authors approached their subject from entirely different perspectives, writing in different eras and for different purposes. Diodorus Siculus, writing in the first century BCE during the late Roman Republic, attempted to compile a universal history of the known world. Plutarch of Chaeronea, writing more than a century later during the height of the Roman Empire, was a philosopher and priest at Delphi who focused on the moral character of famous men. For centuries, readers and scholars have noted the variations, contradictions, and differing emphases between these two foundational texts. When comparing how they describe Alexander’s relationship with his father Philip II, his military strategies, or his personal conduct, the narratives frequently diverge. This divergence has sometimes been misinterpreted as a sign of unreliability or poor historical practice. However, a closer examination of their respective methodologies reveals that these variations are deliberate. They reflect the distinct literary genres in which each author was working, offering complementary rather than strictly competing visions of the ancient world. The study of these texts requires an understanding of the cultural and intellectual environments of the Roman era, where the past was often utilized to explain the present.

What we know

The surviving texts of Plutarch and Diodorus Siculus are cornerstones of classical literature, preserved through centuries of manuscript copying by Byzantine scribes and later printed during the Renaissance. Diodorus Siculus composed his Bibliotheca historica in Greek, aiming to create a comprehensive, chronological account of human events from mythological times down to his own era. Book XVII of this massive work is dedicated entirely to Alexander the Great. Diodorus focuses heavily on the mechanics of empire, military logistics, troop movements, and the broader geopolitical shifts caused by the Macedonian conquests. His narrative is sweeping and didactic, intended to teach lessons about the rise and fall of states and the unpredictable nature of fortune. Plutarch explicitly states in the opening of his Life of Alexander that he is writing biography, not history. His genre is known in Greek as ethopoiia, the depiction of character. Plutarch was primarily interested in the moral virtues and vices of his subjects. He paired the life of Alexander with that of Julius Caesar, intending to show how their innate characters shaped their destinies and the world around them. Because of this focus, Plutarch frequently bypasses major battles with a brief mention, choosing instead to dedicate pages to a seemingly minor anecdote, a witty remark, or a personal interaction. He believed that a casual joke or a small gesture often revealed more about a person’s soul than a siege involving tens of thousands of soldiers. Both authors relied on a shared pool of lost primary sources, known collectively as the Alexander Historians. These included the official court historian Callisthenes, the general Ptolemy, the engineer Aristobulus, the fleet commander Nearchus, and the popular writer Cleitarchus. Diodorus is generally thought to have relied heavily on Cleitarchus, whose account was known for its dramatic and highly rhetorical style. Plutarch, reading widely in the libraries of the Roman Empire, synthesized multiple sources, often comparing them and noting where they disagreed. The preservation of these texts allows modern historians to study not just Alexander, but the intellectual environment of antiquity. The way Plutarch and Diodorus selected, edited, and presented their material demonstrates how the ancient world understood leadership, morality, and the purpose of recording the past. Their works are studied today using philology and textual criticism, methods that trace the lineage of manuscripts to establish the most accurate possible version of the original Greek texts.

What we don't know

Because the primary sources from Alexander’s own lifetime are lost, it is impossible to know exactly how much material Plutarch and Diodorus altered, omitted, or preserved intact. We do not possess the original dispatches sent back to Macedonia, the royal diaries known as the Ephemerides, or the firsthand memoirs of the soldiers who marched to India. Consequently, whenever Plutarch and Diodorus present conflicting versions of an event, it is often difficult to determine which, if either, reflects the historical reality of the fourth century BCE. The exact wording of Alexander’s contemporaries remains largely inaccessible. While Plutarch frequently quotes earlier writers by name, ancient quotation practices were not as rigorous as modern documentary standards. Writers often paraphrased or adapted quotes to fit the stylistic flow of their own prose. Therefore, we cannot be certain if a brilliant retort attributed to Alexander was actually spoken by him, invented by a contemporary flatterer, or polished centuries later by Plutarch to serve a moral lesson. Furthermore, the transmission of these texts through the Middle Ages leaves gaps in our knowledge. Diodorus’s Book XVII survives with some missing sections, known as lacunae, where the manuscript pages were damaged or lost before they could be copied by medieval monks. The exact sources Diodorus used for specific passages are also a matter of ongoing debate, as he rarely cites his predecessors by name in the way Plutarch does. The internal mechanics of how these authors physically composed their works—whether they relied on extensive notes, memory, or teams of scribes—also remain largely hidden from the modern view. We do not know the exact libraries they visited or the specific scrolls they had unrolled before them as they wrote.

What is claimed

In popular culture and casual historical discussions, the accounts of Plutarch and Diodorus are frequently blended together to form a single, seamless narrative of Alexander the Great. This blending often strips away the context of the original authors, treating their texts as a unified database of facts rather than distinct literary works. It is common to see quotes attributed simply to ancient historians, without distinguishing between the moral philosophy of Plutarch and the universal history of Diodorus. There is also a persistent tendency among some readers to view one author as inherently more accurate or reliable than the other. Because Plutarch includes many personal anecdotes and omits tactical military details, his work is sometimes dismissed by military enthusiasts as mere storytelling or gossip. Conversely, Diodorus’s broad, sweeping narrative is occasionally criticized as derivative or overly simplified, with claims that he merely copied earlier, more sensational writers without critical thought. Modern misquotations frequently arise from this misunderstanding of the sources. Phrases and speeches are often attributed directly to Alexander in popular media, books, and online platforms, presented as verified historical transcripts. These claims overlook the fact that such speeches were usually rhetorical exercises crafted by the historians themselves. In ancient historiography, it was standard practice to invent speeches that fit the character of the speaker and the mood of the moment, a tradition dating back to Thucydides. Treating these literary devices as verbatim historical records is a common misstep in the public consumption of ancient history, leading to a distorted view of how ancient texts were actually composed.

What is verified

Textual analysis and historiographical research have firmly established that the variations in the portrayal of Alexander and his father Philip II reflect deliberate methodological differences between the authors. This is the accepted explanation among classical scholars and historians. The differences are not simply errors or signs of unreliability, but the natural result of two writers working in entirely different genres with distinct goals. Plutarch’s approach is verified by his own explicit statements regarding his methodology. He was writing ethopoiia, a character-driven biography designed to explore moral virtues. His selection of material was guided by this philosophical aim. If an anecdote illustrated Alexander’s self-control, ambition, or eventual descent into arrogance, Plutarch included it, regardless of its strategic importance. His work is a study in human nature, using historical figures as the canvas. Similarly, the structure and scope of Diodorus Siculus’s work verify his intent to write a didactic universal history. His focus on the movement of armies, the founding of cities, and the administration of conquered territories aligns perfectly with his goal of recording the grand sweep of human events. Diodorus sought to provide his readers with a comprehensive overview of the past, from which political and military lessons could be drawn. By separating verified textual attributions in ancient manuscripts from popular modern misquotations, researchers can better understand the intellectual environment of antiquity. The surviving manuscripts, housed in archives and universities, confirm what these authors wrote, but they also confirm the literary boundaries within which they operated. Contextualizing these ancient literary methodologies allows us to appreciate Plutarch and Diodorus not as flawed modern journalists, but as sophisticated ancient writers who shaped the legacy of Alexander the Great to fit their respective visions of history and morality.

Competing explanations

• Accepted: Variations in the portrayal of Alexander and Philip reflect deliberate methodological differences between Plutarch's character-driven biography (ethopoiia) and Diodorus Siculus's sweeping, didactic universal history.

What would change our assessment

The current understanding of how Plutarch and Diodorus constructed their narratives is well-supported by the available texts. However, this assessment could be significantly refined or altered by the discovery of new primary evidence. The most transformative event would be the recovery of a lost text from one of the original Alexander Historians, such as the memoirs of Ptolemy or the history of Cleitarchus. Such a discovery is not entirely impossible. The dry sands of Egypt have yielded thousands of ancient papyri over the last century, preserving fragments of lost literature. Additionally, advances in multispectral imaging and artificial intelligence are currently being used to read carbonized scrolls from the Villa of the Papyri in Herculaneum. If a Hellenistic history text were to be deciphered from these or similar remains, it would provide a direct baseline against which to measure the works of Plutarch and Diodorus. Having a primary source would allow researchers to see exactly how the later authors selected, edited, or altered their material. It would clarify whether Diodorus was a faithful copyist of earlier traditions or an active editor who reshaped the narrative to fit his universal history. It would also reveal how much of Plutarch’s moral framing was present in the original sources and how much was his own philosophical addition. Until such a discovery occurs, the comparative study of the surviving texts remains the primary method for understanding the historiography of Alexander.