This chapter questions how European nation-states develop maritime border securitisation strategies that are contingent on the ontology and materiality of terrain on which those borders are established. To do so, it uses ‘infrastructures’ as an analytical tool and explores how oceanic materialities are part of the complexity of migration in/at the Mediterranean Sea, raising questions on how seascapes are transformed into sites of control and conflict. It introduces the concept infrastructural containment to address the spatio-material strategies deployed by nation-states to further strengthen borders and contain ‘clandestine’ maritime crossings. The chapter questions how containment of migrant mobilities is configured through the fluid, vast and turbulent nature of the ocean and how its often hostile terrain plays an active role in the production of border infrastructures by becoming an environmental boundary. It argues that an infrastructural approach to water allows for additional ways of understanding technologies of containment at the Mediterranean Sea and the challenges posed by the ocean’s wetness and fluidity resists also the EU’s attempts to establish rigid territorial boundaries. This chapter underscores the complex and evolving nature of maritime borders, prompting a critical reflection on oceanic governance, which often relies on land-centric approaches to territorialisation.