In 1722, following a request by King João V of Portugal, two missionaries from the Naples College traveled to Lisbon: Giovanni Battista Carbone (1694-1750) and Domenico Capassi (1694-1736). The aim was to employ the two astronomers in cartographical work on the state of Maranhão, in Brazil. In this lecture, Luis Tirapicos, a PhD candidate in history of science at the University of Lisbon, Portugal, will discuss the work of these and other Jesuit astronomers in the wider context of the Portuguese-Spanish dispute of borders between its South American colonies.