The Casamance region of Southern Senegal is characterised by a deeply entrenched dualism that shapes linguistic and cultural expression. While most cultural practices and important parts of the linguistic repertoires of its inhabitants are shared throughout the region, these regional convergences have not led to the emergence of a shared lingua franca that could result in a new, creolised identity. Despite shared linguistic repertoires, distinct local identities are also upheld in this region through the maintenance of small, often village-based languages, resulting in high individual multilingualism and great linguistic diversity in the area. I explore the historical development of this cultural and linguistic ecology, tracing it back to the need for expressing flexible alliances through the situated creation and transcendence of boundaries in a Frontier society. I discuss the social mechanisms that nurture this type of multilingualism and investigate how its longstanding patterns are transformed 1 The ideas presented here emerged during the interdisciplinary research project "Pots, plants and peoplea documentation of Baïnounk knowledge systems", funded by the DoBeS programme of the VW Foundation from 2010 to 2013. My heartfelt thanks go to the colleagues and students working with me in this project-Amadou Kane Beye, Alexander Cobbinah, Cheikh Daouda Diatta and Moustapha Sall. The emerging hypotheses on multilingual language use and the ideologies fuelling it resulted in the ongoing Leverhulme Research Leadership Award Project "Crossroads-investigating the unexplored side of multilingualism" in Casamance. I gratefully acknowledge the support of both funders. I am deeply indebted to my students and colleagues