This paper aims to analyze some aspects of the connection between city, space and law. Using the concept of "urban fact", that is more specific than "city", the autonomy of urban spaces is examined as emancipation (from the State, from the territory as a hierarchical criterion, from the sources of law) and as construction (of a new balance between public and private spaces; of a different balance between city and nature; of a new model of citizenship), highlighting how urban commons clearly show some aspects of the great dichotomies of contemporary law: public-private, law-economy, State-market.