The present article studies the foundation of San Juan de la Frontera de Paspaya in the jurisdiction of the Real Audiencia de Charcas in the second half of the sixteenth century, framing the event as part of the wider process of incorporation of new geographies into the Spanish monarchy. The documentation analysed describes the complex negotiations among various agents organised around networks of patronage and hierarchies, including Spanish frontier captains and their men as well as the Andean indigenous communities of San Lucas de Payacollo and the Guaraní-speaking Chiriguanaes. The article provides some insights into the manner in which frontier spaces of the Catholic monarchy were politically constructed and equipped with relations and institutions in the late sixteenth century.