The Syracusan Revolution of 466 BC ended a period of tyrannical rule in the city and ushered in a prolonged period of democracy and prosperity. Syracuse had been ruled by a Tyrant since 485 BC when Gelon, Tyrant of Gela, took advantage of civil strife in the city to take control. He earned great public support for his role in the defeat of the Carthaginian invasion of Greek Sicily in 480 BC and his victory at the battle of Himera. He was followed by his brother Hiero, who maintained his power until his death in 467 BC despite gaining a poor reputation.
Hiero was succeeded by his brother Thrasybulus. The new tyrant was even worse than his predecessor. According to Diodorus he was violent and murderous, and began to execute or exile citizens of Syracuse so he could seize their property. At the same time he employed a large number of mercenaries.
Thrasybulus's efforts failed to prevent the citizens of Syracuse from rebelling. They seized a suburb of the city called Tychê, outside the fortified are of the city. They then called for help from most of their neighbours. The tyrannies of Akragas, Gela and Himera had recently been overthrown, and the newly freed cities all sent help to the rebels. They also received support from the city of Selinus, a Greek settlement in the Punic area of influence in the west, and from the Sicels (the native inhabitants of eastern Sicily, by this point pinned into the interior). Thrasybulus had 15,000 men, but the rebels and their new allies managed to raise a force capable of effectively besieging the Tyrant in the fortified area of Achradina and the 'island' of Ortygia (the headland between the Little and Great Harbours). The rebels had also been sent a significant number of ships.
Thrasybulus made two attempts to defeat the rebels. First he led his fleet out to sea, but he was defeated in a naval battle and forced back into Syracuse. Next he led his army out into the suburbs, but once again he suffered a defeat and had to retreat back into the fortifications.
After this second defeat Thrasybulus decided to negotiate with the rebels. He renounced all power and retired to Locri in southern Italy where he spent the rest of his life as a private citizen. His mercenaries were allowed to withdraw from the city. The successful rebels now founded a democratic government in Syracuse, which survived for sixty years, before finally being abandoned in the face of a Carthaginian invasion. The Syracusan democracy successfully resisted the Athenian invasion of 414-3 BC, and helped free most of the Greek cities of Sicily. There was a short period of instability in the aftermath of the overthrow of the tyrants, with a war against the Mercenaries in Gela and Akragas, and a civil war in Syracuse, again against a force of mercenaries, before a period of relative peace began in Greek Sicily.