This article explores the nineteenth-century history of ship’s ballast to study global maritime mobility ‘from below’, both socially and materially. Though mostly overlooked by contemporaries and historians alike, ballast was both a necessary resource for and a constraint on sea travel. This article examines ballast in four steps. First, it defines ballast in terms of its function, materiality, and value. Second, it studies ballast in the littoral zone, where specialized ballasting organizations depended on precarious labour and where both its production and disposal became entangled with environmental agendas and concerns. In a third step, the article focuses on ballast at sea, where it materially and sometimes detrimentally impacted the experience of ‘being in transit’. Finally, the article considers the transition to water ballast as an example for the persistence and staying-power of seemingly obsolete technologies and associated labour regimes. Ballast was an obscure but powerful enabler of sea travel. Maintaining this connectivity rested both on the widespread mobilization of labour for ballast practices and on the global movement of vast amounts of otherwise useless weight.