Transformations of Derry/Londonderry’s medieval city walls during the twentieth century have shaped an urbanism of segregated settlements within a city of religious confrontation. The heritage of military blockades, peace lines and watchtowers imposed upon the city’s Walls has influenced the disintegration of public space and created areas of no man’s land around the peripheries of the monument. The aim of this paper is to examine physical transformation and trace the consequences of urban planning regarding the historic city Walls. This change includes the shifting of residential settlements in the Bogside/Fountain areas and the movement of Protestant settlements towards the Waterside of Derry/Londonderry. The history and heritage of the Walls are analysed by focusing on four periods: 1600, when the first medieval walls were constructed; the housing crisis of 1948; the 1968 urban area plan and the beginning of the ‘Troubles’; and the present day. This analysis offers an understanding of the spatial relationships between enclaves and the monument over key moments of conflict and political change. The paper reveals that the manifestations of the Walls have aided in the further division of religiously segregated communities in Derry/Londonderry.