The Jura Arc, animated by intense cross-border exchanges from 1789 to 1798, is a privileged region of observation for conducting a transnational study of relations between France and the Principality of Neuchâtel, two French-speaking territories with contrasting geopolitical developments. To what extent do these exchanges contribute to the affirmation of national feelings of belonging that are at odds with traditional hierarchies? Border socialization, facilitated by the absence of war between these two countries, encouraged crossborder commitments which, by their pace, nuance the idea of a clear shift from the promise of a borderless Europe to an increase in chauvinism. The intertwined history of the Jura Arc reveals that the revolutionary period was a founding moment both for the territorial marking, the speeches and iconography that accompanied it, and for the emergence of a watchmaking activity that became a link between France and Switzerland.