The twenty-first century arises, due to the revolution in transports and communications and the different international agreements and alliances, as a stage in which the international territorial frontiers seem more open than before. This study approaches to one of these frontiers to look how the people that inhabit in the borders live one of these agreements: the building of a unique economic and political European space. It is an ethnographical study of the shire of the Cerdanya, crossed since 1659 at the very middle of its main valley by the French-Spanish dividing line. Despite historically the frontier has created contacts and movements that have crossed it; a reality marked by the border is discovered throughout the text. The discourses about a Europe without frontiers and a Cerdanya nationally Catalan or, at least, unified, face the competition of interests, the allusions to the international dividing line (though it would be for complaining), the desire or the necessity of crossing it and, especially, a daily experience marked by schedules, news, the education system, prices, taxes, wages, pensions, public services, the army, communication routes and linguistic usages that have been taken as different projects of state-nation confluents to the territory of Cerdanya were developed. The text shows how, paradoxically, the process of construction of a Europe without frontiers has stressed the meaning of the territorial division of the shire, which has proved the validity of the modern model of state-nation to the formation of national identities.