How did Venice change from a duchy into a republic during the 12th century?

During the 12th century, Venice underwent a significant political transformation, evolving from a duchy into a republic. Between 1140 and 1160, in response to the demands of its expanding territory and growing economy, the city reorganized its political structure to shift power away from the doge.1

Key aspects of this transition included:

• Loss of Monarchic Power: The doge lost his monarchic character, transitioning into an official role, although he retained prestigious titles.1
• Establishment of the Commune: A commune was formed to assume the state's powers, functions, and prerogatives.1
• Centralized Governance: Political and administrative authority was placed in the hands of the Great Council, which initially consisted of 45 members.1
• Executive and Judicial Oversight: A Minor Council of six members was established to exercise executive powers alongside the doge, while various magistrates were appointed to handle administrative and judicial functions.1

By the 12th century, the Venetian aristocracy had placed strict limits on the doge, requiring him to swear an oath that restricted his freedom of action and ensured he remained subject to the law.2