The History of the Peloponnesian War, also known as Histories, recounts the war between the Athenian alliance (called the Delian League by modern historians) and Sparta and its allies (called the Peloponnesian League by modern historians), which took place from 431-404 BC. Composed in the 5th century BC by Thucydides (c. 460-400), it is the first attempt to apply empirical research and analysis to understanding contemporaneous human events. For this reason, the text is inextricably linked with its author, who has been called one of the fathers of history. The History of the Peloponnesian War ends in mid-sentence in 411, seven years before the end of the war and 11 before Thucydides—who served as an Athenian general before being exiled in 422, for failing a mission—is believed to have died.

As with any ancient text, much about the work is contested and much remains unclear. Scholars note that Thucydides’ style is uniquely dense and complex and thus challenging to translate. This guide refers to the Penguin Classics edition translated by Rex Warner.

Scholars disagree about when the eight books that make up the history were composed, in particular whether they were written over the course of many years or after the war ended in 404. Though several of the books appear to be in-progress drafts, the eighth is thought to be the most incomplete, organizationally, and may have been a collection of notes.

To facilitate study of the text, scholars have developed a system of enumeration to correspond between the original Greek and translations: Each book is made up of sections of varying lengths that are called chapters. Warner’s translation groups related chapters within each book under subheadings, though these subheadings do not appear in the original Greek text.

Book 1 is the longest in the history and covers the broadest swath of time. Thucydides introduces himself and his method and provides overviews both of the Hellenic people across time and, more specifically, of the Peloponnesian War’s numerous inciting events, which began immediately following the end of the Persian War. He describes three key disputes among allies of the two states, as well as other grievances and confrontations, but believes the war’s singular cause was Sparta’s fear of Athens’ growing influence in the Hellenic world. The book ends with Sparta and its allies voting to declare war on Athens.

In Book 2, the war begins with Thebes’ invasion of Plataea and Athens’ involvement on its behalf. It covers the first three years of the war and is characterized by skirmishes and battles among allied states stretching across the Hellenic-occupied region. A series of victories at sea bolsters Athens’ confidence, while Sparta remains the stronger power on land. The plague devastates Athens and claims the life of its charismatic leader, Pericles.

Book 3 concerns events of the fourth through sixth years of the war. Athens subdues a revolt in one of its allied cities, Mytilene, on the Aegean island of Lesbos, then debates how to punish survivors. An initial decision to punish guilty and innocent equally is rescinded after an impassioned debate in the Athenian assembly. Besieged Plataea suffers famine and is forced to surrender to Sparta, and civil war breaks out in Corcyra, between democratic and oligarchic factions. Athens sends ships to Sicily, and Sparta cancels a planned invasion of Athens due to a series of earthquakes. 

In Book 4, following the seventh through ninth years of the war, Athens achieves victory at Pylos and Sphacteria, prompting the Spartans to seek a peace treaty. Athenian general Cleon argues that Athens should demand land back from a previous war, and talks break down. Sicily’s fractured states hold a peace conference to discuss protecting themselves from Athens’ aggression, and Spartan general Brasidas incites revolts among Athenian allies. Boeotia defeats Athens at Delium, which Brasidas subsequently captures. Sparta and Athens establish an uneasy one-year truce that promptly breaks down.

Book 5 spans a longer stretch of the war than the previous three books, covering the tenth through sixteenth years. Thucydides recounts two significant battles, at Amphipolis and at Mantinea, with Sparta victorious in both. Following the battle at Amphipolis, Sparta and Athens both seek peace and, with the Peace of Nicias, enter into a treaty and alliance. Argos contrives to become the leader of Hellas. Despite the peace treaty, political, military, and diplomatic maneuvering continues among the Argives, Athenians, Spartans, and their allies. Athens demands that neutral Melos join the Athenian alliance. When it refuses, Athens massacres the island in what is called one of the city’s worst atrocities.

Much of Book 6, during the sixteenth and seventeenth years of the war, takes place in Sicily. The Athenians debate whether to send an expedition to conquer Sicily. Those in favor, including general Alcibiades, win the vote, and the city sends off an enormous fleet with pomp and ceremony. In Sicily, Syracusans prepare to meet the Athenian invasion. Alcibiades is recalled to Athens to face charges he defaced religious statues, but he escapes to the Peloponnese. Athens achieves victory at Syracuse, and the Sicilians appeal to Sparta for aid. Athens continues to achieve success in Sicily, and Sparta prepares to send a general, Gylippus, and Corinthian ships to Sicily. 

Athens’ failed expedition to Sicily, which occurs in the eighteenth year of the war, occupies the bulk of Book 7. Spartan general Gylippus brings allied Corinthian ships to Sicily to support the Syracusans. Athens suffers a devastating naval defeat, and its navy is forced to retreat by land, where they are eventually trapped and captured. The entire expedition is killed or enslaved.

Book 8 returns to Attica and the Aegean islands of Chios and Samos to examine the consequences of Athens’ defeat in Sicily. Sparta establishes a shaky alliance with Persia, while Athens loses critical ally Chios to revolt, after which the island descends into civil strife and famine. An oligarchic coup topples Athens’ democracy in 411, and the Athenians recall disgraced general Alcibiades, who collaborated with Sparta and Persia after his exile from Athens. Athenians win a naval battle and regain some of their confidence. The book ends abruptly in 411, as Tissaphernes seeks to strengthen his alliance with Sparta.