The Western Pyrenees were for the Navarrese an area of livestock grazing during the central Middle Ages, thanks to age-old usage of the mountain passes, along with the benefits of lower altitude lands such as Ultrapuertos in Navarre. In contrast with the surrounding mountainous areas, these lands were well suited to transhumance. Therefore, we consider livestock flows essential to understanding the geographic features of this region that bordered the important French, Navarrese and English medieval kingdoms of that period. This article seeks to identify a whole network of relationships that go from the principal livestock movements to gains obtained by local authorities or the king by means of taxing or leasing pastures. Also pertinent are the commercial dynamics affecting livestock in regional markets on both sides of the Pyrenees. This signals an area of exchange and collaboration between the people of Navarre, Labourd and Béarn, in a relationship which has survived until the present. One can see this in the fact that some treaties rooted in the Middle Ages have survived until today, such as the facerias
