Peloponnesian War — Timeline & Key Events

Thucydides insists the war’s truest cause was structural—Spartan fear of Athenian growth made conflict inevitable despite paper guarantees in the Thirty Years’ Peace ^[1][12][16]. Arbitration clauses offered de-escalation in theory, but alliance flashpoints—Corcyra, Potidaea, Megarian sanctions—showed that prestige, honor, and deterrence logic often outran legal frameworks ^[12][16]. In that light, the Theban night attack on Plataea is less a provocation than the first crack in a strained architecture ^[1].

Yet contingency mattered. Leadership deaths (Pericles to plague, Brasidas and Cleon at Amphipolis) and singular events (Sphacteria’s Spartan prisoners) redirected incentives toward truce or escalation ^[1][16]. The Peace of Nicias reflected this recalibration, but its erosion after Mantinea reveals how quickly fear reasserted itself ^[16]. Modern scholarship emphasizes these decisions and miscalculations: the path to war and defeat was paved not only by structures but by leaders choosing, and often misreading, the moment ^[10][11][13].

Athenian sea power rested on finance: allied tribute lists carved in marble implied steady pay for rowers, timber for hulls, and dockyard maintenance ^[9][20][16]. With Pericles’ strategy anchoring survival to the fleet, victory at Rhium/Naupactus (429) and leverage at Sphacteria (425) were not just tactical feats—they were budgetary affirmations ^[16]. The tribute system’s visibility made imperial power legible and, to allies, onerous ^[9][20].

Sparta’s answer was Persian money. Tissaphernes’ subsidies started the shift; Cyrus the Younger’s direct, punctual funding from 407 transformed Spartan fleets into sustained instruments of war ^[16]. Regular pay retained crews between seasons, enabled repairs, and supported offensive operations in the Hellespont where Athens lived on imported grain ^[11][16]. The chain is clear: inscriptions to pay; pay to crews; crews to victories—culminating in Aegospotami and the ruin of a cash-starved opponent ^[3][11][16].

Athens reengineered geography with stone: the Long Walls yoked city to port, turning invasions into smoke and inconvenience rather than capitulation ^[1][16]. Maritime control of the Hellespont acted as a grain umbilical, so battles like Cynossema and Abydos in 411 and Cyzicus in 410 were really logistics fights whose stakes were winter bread, not just laurels ^[11][16]. Geography narrowed strategy—command the narrows or start starving.

Sparta adapted. Decelea’s year-round fort in 413 made Attica bleed continuously—fields idle, slaves fleeing, revenues shrinking ^[1][16]. The combined effect of Decelea ashore and Persian-backed fleets afloat pinched Athens from both ends: land labor fled to the Spartan post while sea lanes came under disciplined attack. When Lysander struck at Aegospotami, he didn’t just sink ships—he severed a city’s circulatory system ^[3][16].

War exposed how far Athenian democracy could flex before it fractured. The 411 coup of the Four Hundred condensed authority in a bid to manage crisis; the subsequent Five Thousand tried to broaden participation while preserving wartime efficiency ^[16]. Naval crews at Samos and Athenian victories in the Hellespont helped pull politics back toward democratic forms, illustrating how battlefield fortunes could reconfigure legitimacy at home ^[11][16].

But stress warped norms. After the hard-fought win at Arginusae (406), the Assembly executed six victorious generals over failed rescue attempts in a storm, trading due process for catharsis ^[3][16]. The final humiliation—surrender in 404—brought the Spartan-backed Thirty, whose terror underscored how thin civic safeguards had become ^[3][16]. Thucydides’ reflection that “war is a violent teacher” captures the pattern: emergency logic corrodes the procedures it claims to save ^[1].

Athenian rhetoric framed empire as both ideal and necessity. Pericles’ Funeral Oration promised meaning in sacrifice and an open, confident city; the Melian Dialogue reduced choice to force and interest—“the strong do what they can” ^[1]. That moral-psychological mix primed voters to see Sicily as a prudent expansion rather than a bridge too far, especially under Alcibiades’ electric advocacy ^[6][16].

The annihilation at Syracuse shattered the story Athens told itself ^[1][16][17]. What seemed like strategic diversification became overextension: lost ships, lost men, and lost credibility. The subsequent Spartan fortification at Decelea and Persian-financed naval challenge show how enemies exploit ideological overreach once the spell breaks. The lesson stretches beyond 404: ideas can mobilize resources faster than institutions can absorb failure ^[1][16].