In the 1850s, Portugal initiated an ambitious public works program spearheaded by railroads. In this article, I analyze how policymakers (congressmen, government officials, engineers, and military officers) debated and managed the construction and operation of the Portuguese railroad network using the theoretical framework of critical infrastructure. I show that railroads were deemed critical to modernize the country, draw it closer to the European core nations and further from the periphery, and to attract traffic to the Portuguese harbors. The absence of railroads was considered a vulnerability that could jeopardize Portugal as a nation and it fostered a sense of urgency that motivated policymakers to act, to a large extent, hastily. The construction of the network brought about other vulnerabilities that, for different motives, could threaten the future of the country. In a parallel way, the implementation of the system was marked by vulnerabilities that originated within or surrounding it, which limited its technical potential. Balancing between a literature review and the use of primary sources (parliamentary debates, technical reports, the press, and photography), I argue that the criticality associated with railroads, as a sociotechnical construction, was central to motivate their construction, but different vulnerabilities, inherent or external to the system, limited their influence and the advantages touted by its promoters.