In the sixteenth century, excluded by the monopoly from colonial commerce, several Basque and Cantabrican ports developed a measure of vitality from trading networks founded upon the commerce of the export of raw materials to northern and western Europe. Many have considered the Asturian, Cantabrican and Basque ports merely as outports of a vast and complex region; this is a false assumption. It is no easy task because entwined in this drama are some of the not fully understood processes that first precipitated the rise, then the rapid decline of Spanish imperial economic and political hegemony (Gentil da Silva,1967). On the other hand, to understand the rise of Castile and particularly its ports in the earlier part of the same century, one has to grapple with processes including the consolidation of Spain as a powerful multinational state and the evolution of Spanish national identity (García Fernández, 1985). That is not all. Much has been written about the Spanish wool trade, which was Castile’s early engine of growth (Phillips and Phillips, 1997). While not subject to a colonial monopoly, the wool trade was operating under the aegis of cartel regulations of the Mesta, a sheep-owner’s guild, which was a monopoly in itself (Klein, 1920). It was also administered by the Consulado at Burgos upon which its later Sevillian counterpart was modelled. Spanish merchants resident outside the peninsula acquired commercial expertise later put to better effect in the New World. It was, at least for some, a training ground put to good use later at the Sevillian metropole. For these reasons, it is pertinent to assess the contribution of the settlements and ports of this complex region to Spain’s Atlantic commercial endeavour. It starts with a consideration of the Atlantic wool trade and its contribution to urban growth and port development. There is then an assessment of the dynamic relationships that emerged between the ploughmen, cowmen, shepherds of Castile and the Atlantic. The focus is then set on the rise and demise of the chief urban centres involved in the trade and concludes by examining the implications of the declaration of Madrid in 1561 as capital of Castile and the Atlantic. After all, Castile was a major producer of raw materials; wheat, wine wool and wood exports underpinned the evolution of many ports and here the tone is set for the later consideration of the contributions of two specific ports namely Santander and Bilbao.