This paper deals with the spatial implications of the French sanitary policies in early colonial urban Senegal. It focuses on the French politics of residential segregation following the outbreak of the bubonic plague in Dakar in 1914, and their precedents in Saint Louis. These policies can be conceived as most dramatic, resulting in a displacement of a considerable portion of the indigenous population, who did not want or could not afford to build à l’européen, to the margins of the colonial city. Aspects of residential segregation are analysed here through the perspective of cultural history and history of colonial planning and architecture, in contrast to the existing literature on this topic.