Abstract
After signing the 1777 Treaty of San Ildefonso, Spain and Portugal sent joint expeditions to demarcate their South American borders, as they had done a quarter century earlier. Focusing on the activities of Spanish commissioner Francisco Requena in western Amazonia in the 1780s and 1790s, this article shows that such efforts were not limited to confirming in loco the lines drawn in European courts. I demonstrate how Indigenous populations played on Iberian rivalries to maintain their autonomy and negotiate their resettlement. The very interactions between commissioners and Indigenous peoples intensified the porosity of border spaces. Because commissioners believed that sovereignty was defined through monarchical loyalty rather than simply lines on a map, they contributed to the movement of people and goods across the dividing line that they intended to create, making the border even more permeable to Indigenous claims to territoriality and cross-border interactions.
