From the Belvedere of the Philharmonie, the Orgues de Flandre almost hide the Sacré-Cœur Basilica. This architectural complex, built between 1973 and 1980, is located in the 19th arrondissement of Paris. The German architect Martin Schulz van Treeck imagined new social housing thanks to an invention, the relatoscope. Modelled on the endoscope, this device allows architects to have another vision of a model. On about 6 hectares, he created four towers, called Sonata, Fugue, Cantata and Prelude, two 15-storey buildings with outward or inward steps and other lower buildings for a total of 1,950 dwellings.