Washington, D.C. was the first American planned city of its size and one of the first attempts at a spatial organisation of the nation’s political objectives. This thesis argues that Pierre L’Enfant’s 1791 plan for the city is a unique example of eighteenth-century speculative development, that assimilated dominant European garden and urban planning traditions, reflected a critical transition in attitudes towards nature and landscape, and produced an unprecedented symbolic framework for the balance of republican values and federal objectives. I use a review of the development of the plan and an analysis of its distribution of space to locate the city within a wider context of continental expansion and the consolidation of national union. In the first part of this thesis I trace three aspects of this context: first, the plan’s relationship to contemporary patterns of land management, survey and territorial settlement; second, the eighteenth-century significance of nature within political thought and the manifestation of these ideas in the garden and landscape precedents available to the architect and his contemporaries; and third, the shift from representations of monarchy to celebrations of presidential authority, evident in L’Enfant’s work. In the second part I conduct a drawn dissection of the structure of the 1791 plan and provide a new interpretation of the primary orientation of the city, the distribution of ceremonial spaces, and the projected character of the commercial and residential urban fabric. Through a conceptual-historical reconstruction of the relationship between the plan for the capital, national expansion and American democracy, my project seeks to recover the significance of Washington, D.C. as a seminal reflection of the collision of a European urban and landscape tradition with the formation of an American political ideology.