James Hobrecht's Berlin extension plan of 1862 and its architectural component, the Berlin block, continue to define Berlin's current urban structure. The urban structure which these graphic documents helped to deliver persisted despite being rejected through much of the twentieth century. Despite its significance, research on the Hobrecht plan is scarce, and many interpret the plan through its historical context. By contrast, this paper argues that the Berlin block cannot be reduced to representations through its urban plan and architectural component. Instead, they provide a specific urban rationality that poses the question: What is a city? Françoise Choay identified a new urban figure in Ildefonso Cerdá's urban theories, a figure that comes to underlie subsequent theorisations of the urban. The paper argues that the Hobrecht plan and its component block can be read as the graphic and spatial counterpart to Choay's textual figure of the urban.