During the first half of the fourteenth century, the Order of Santiago was able to set up and organize its own domain in Portugal, composed of extensive land holdings located mainly to the south of the Tagus estuary. Here, the Order both established coastal commanderies and developed pasture lands in an area where cross-border cattle movements from Castile would provide an important source of income. This article intends to shed light on a broadly neglected area of the Portuguese historiography on the Military Orders: transhumance. This was an important activity which itself explains the founding of the Military Order of Santiago’s commanderies around one of the most important areas of pastureland in the Iberian Peninsula – Campo de Ourique – established to control the main routes of transhumance and ensure the collection of substantial rents and other charges. To achieve the aforementioned aim, this research draws upon documentation and archives hitherto insufficiently explored to this end.