Casa Batlló was nearly demolished. Josep Batlló, a textile manufacturer, bought a plain 1877 block on Passeig de Gràcia — built by Emili Sala, one of Gaudí's own teachers — and meant to clear the site. Gaudí persuaded him to keep the old shell and rebuild everything else, and Batlló gave him a free hand. Between 1904 and 1906 he refaced the lower floors in Montjuïc sandstone carved into columns shaped like leg bones, hung cast-iron balconies that look like masks, and clad the wall above in trencadís: broken ceramic and glass discs, warm near the street, blue at the roofline. Barcelona called it the Casa dels Ossos, the house of bones.
Inside, straight lines are rare. The oak doors curve, the stair rail winds up the well in one unbroken twist, and the plaster of the main salon ceiling spirals outward from the light fitting at its centre. Gaudí added an attic of whitewashed catenary arches and, above it, a roof of scaled tile with a cross-topped turret. The Batlló family lived on the main floor and let the rest as flats. It is a house-museum now, part of the UNESCO listing of Gaudí's work, and the pavement outside is among the most crowded in the city.