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Why did Milan form an autonomous commune in 1045?

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People walk and shop inside the ornate Galleria Vittorio Emanuele II in Milan, Italy, with its glass-domed roof, decorative mosaics, and luxury store entrances. — Milan Shoppers in the Galleria Vittorio Emanuele II, Milan.

In 1045, Milan established itself as an autonomous commune (comune) primarily due to two factors: the tensions generated by the temporal authority of the archbishops and the city's overall growth and increasing stability.1

During this period, the political power of the archbishopric had reached its peak under Ariberto da Antimiano (1018–1045). The transition to a communal government allowed the city to implement permanent and autonomous administrative structures, marking a significant shift in how Milan was governed. This development was part of a broader trend in northern and central Italy where cities sought greater independence, though the specific motivations for such shifts were complex and varied based on local social and political dynamics.12