Starting in the late 1870s and until the eve of World War I, Portugal proposed the construction of several railways in its colonial territories in Angola, Mozambique, Goa (India), and Macao (China), following in the footsteps of other imperial nations. By 1914, the main trunks of the system were laid down. Most historiography about Portuguese colonial railways usually ponders the logic behind their debate, implementation, and operation as utterly technological and focuses primarily on their consequences, taking railways for granted, or black-boxed. Some more recent studies have moved the focus to the sociotechnical context and to the utopias and hierarchies of power of the time to analyse the construction specific lines. In this chapter, I add technical reports, parliamentary debates, and photography to this literature to offer an overarching perspective about the sociotechnical construction of the Portuguese imperial railway system. I propose to open the proverbial Latourian black box of the Portuguese colonial railway system and to investigate the prospects, urgencies, and subsequent decisions of the different system-builders and stakeholders involved in the debate and construction of railways in the Portuguese colonies. I follow engineers, colonial authorities, legislators in parliament and government, and the financiers and policymakers of neighbouring colonies (mainly British) to analyse in what manner they influenced the layout of the system. I show that engineers played a key role in the planification of construction, but a substantial part was due to non-technical factors, namely the geopolitics of the New Imperialism of the late nineteenth and early twentieth centuries. Additionally, I show that the concerns of native peoples were disregarded, but they, nonetheless, influenced the decision-making process of some particular tracks (namely in Angola and China).