The debacle of the siege of Syracuse fatally undermined the city-state of Athens, leading to its eventual defeat and sacking by rival Sparta. It began, ostensibly, as a dispute resolution exercise on behalf of another Sicilian city, Segesta. After much disagreement, the expedition’s three ill-matched commanders diverted to claim the richer prize of Syracuse. One of the leaders was advised he had been sentenced to death in absentia: he promptly fled to Sparta. After having the better of initial exchanges on sea and land, the Athenian forces decided to overwinter in Sicily, summoning reinforcements. The Syracusans, meanwhile, sent for help from Sparta, which sent a large fleet. After a battle of attrition, with both sides building walls, the Athenian fleet was finally trapped in the harbour and destroyed. Trapped, the remaining Athenian land troops were chased inland and killed or enslaved. Athens’ naval might was irrevocably undermined.