The increasing vulnerability of Small Island Developing States (SIDS), and in particular low-lying South Pacific nations, due to climate change necessitates innovative and sustainable adaptation strategies. One such strategy is the development of floating cities, which offers the promise of mitigating the effects of rising sea levels and the incursion of water in urban centres, while ensuring the continued socio-economic stability in the region. This paper argues that the creation and enforcement of legal frameworks supporting floating cities needs to be examined at international law. While steps have been taken to fix maritime baselines to set out the territorial waters of island states subjected to inundation, the legal concept of Statehood in international law requires us to address the fundamental question of a ‘defined territory’ and how the ambit of the definition of ‘territory’ could be addressed by floating structures. This paper argues that the recognition of floating structures as ‘territory’ is crucial as it allow states to avoid costly and significantly delayed responses through land reclamation. To aid this recognition of floating structures as ‘territory’, this paper argues that such recognition should be treated as an erga omnes obligation—an obligation owed by states to the international community as a whole. This paper examines the international legal precedents, proposed legal frameworks, and the technical solution of floating cities to argue for the legal necessity of such urban interventions. It concludes by asserting that the recognition of legal support for floating cities as an erga omnes obligation is not only a legal necessity but also a moral imperative to ensure the survival and prosperity of vulnerable populations in the face of global climate change.