The trans-European transport network (TEN-T) is a key factor in the relationship between railway development and urban growth in Europe, with a tangible impact on urban morphology. In this scenario, the aim of this article is to analyze how the Mediterranean Railway Corridor (EU’s TEN-T strategy) is inducing new processes of railway integration in the urban system located along the Spanish Mediterranean coast. Our working hypothesis is based on the analysis of three vectors that are modifying the relationship between high-performance rail networks and cities, using new processes that have been overlooked by most of the existing scientific and EU grey literature. Firstly, the development of a trans-European transport network (TEN-T) is driving new and complex rail projects that are associated with achieving the full interoperability of the trans-European rail corridors. Secondly, the European liberalization of passenger transport is promoting rail operations with a strong urban and morphological impact, due to the resulting increase in rail services. Finally, the European response to the consequences of the 2020 COVID-19 pandemic has made it possible to launch large-scale financial operations aimed at sustainable transport projects, including rail projects. We have carried out an analysis of the academic and institutional literature and we have also considered three case studies along the Mediterranean Corridor in Spain: Barcelona, Valencia, and Murcia. For each one, we present the structure of the current rail networks, the ongoing urban integration projects driven by the Mediterranean Corridor, and the resulting implications for urban morphology, as well as the opportunities they bring from a socio-economic perspective. Therefore, we argue that there is a triple substantial change: the significance of rail and urban projects (from the national scale to throughout the European Union), the operational network (from the domestic high-speed network to the TEN-T network), and funding (from state self-financing to European CEF and RRF funds). Nonetheless, further research activities are needed to assess how the revision of the TEN-T regulation strategy will affect the urban–railway relationship.