The image of the symposium corresponds to the roof of the Pedrera with its chimneys, ventilation shafts and “badalots” (roof casings of the stairwells), where Gaudi used the timbrel vault, covering them in most cases with a “trencadís” (ceramic mosaic) that adapts to curved surfaces. The timbrel vault is, in fact, a genuine ancient technique used for covering spaces with “maó de pla” (flat bricks) ; also called “Catalan brick” because it was widely used during the XIX century in Catalonia. Gaudí took this technique to its highest expression.