Reports such as these scratch the surface of a raft of indexical measures to ascertain the material urban damage inflicted on the city. The product of an array of statistical measures and forms of knowledge capture, the numbers express a plethora of bureaucracy aimed at knowing the impact of the Blitz upon objects that were almost unknowable, resisting this gaze. This essay considers how such techniques, among with others, came to compose a kind of architecture. This was not simply in the concrete forms of bunkers or shelters, but as an apparatus of urban protection whose task was to ensure that the city would live on (Gollin 1984, Charlton 1935, Billing 1916).