In this article, our aim is to explore the importance of different factors in the explanation of the sustainability of common lands over the long-term. We will analyze the importance of the rules (formal and informal), but also the making of identities by local communities regarding common lands. We also explore the role of changes in the environmental and economic functionality of common lands. Our case study is located in Galicia in Northwest Spain. We will analyze a particular example of common lands not recognized by law until 1968, trying to show how the legal clarification and the construction of clear systems of rules are not sufficient to explain the sustainability of the commons. The Spanish liberal state did not accept the singular character of the Galician common property since the Cadiz parliament assimilated the Galician commons to the municipal property prevailing in other parts of Spain. From 1960 to 1985, the situation reversed due to a conflict between Galician communities and the Franco regime. In this conflict, two productive alternatives confronted each other: the productive use of forest lands defended by the forest services of the regime and the use of the land for livestock. The victory of the communities did not succeed in the growth of grazed lands, but neither did the forest option. On the contrary from 1970 onwards the common lands lost their productive functions and many left the common lands.