This chapter studies how the annexation of Portugal by the Spanish Habsburgs between 1580 and 1640 impacted its military technology and especially its artillery. By focusing on the documentation from the Spanish artillery administration, it highlights the strategic role that Portugal, and especially Lisbon, came to play in the military organization of the Spanish monarchy. Soon after the annexation, the royal Council of War in Madrid took over the leadership of artillery matters regarding Portugal and integrated it into the wide administrative network of the Habsburg Monarchy. By entering the orbit of a state which, according to Parker, was a pioneer actor of the military revolution, Portugal gained new institutional structures and benefited from a widely transnational circulation of knowledge and experts. The artillery personnel of Portugal soon included seasoned Castilian officers, Italian engineers, and gunners and gunmakers coming from the four corners of Europe, while some Portuguese technicians got involved in Spanish imperial dynamics, being sent to Cuba with the mission to create a new gun foundry. The transfer of technology and knowledge was strengthened by the implementation of artillery lessons taught by Italian and Castilian masters, on the model of the schools of the gunners that the Spanish monarchy opened in other artillery hubs, such as Milan, Palermo, Burgos, and Seville.