The catenary arch prevents it from having to be reinforced from the outside to counteract the force it supports. It has a very special feature: it can bear much more weight than the rest. Gaudí discovered how easy it was to build hyperbolic paraboloids, for which masons needed only two rulers and a string.

The catenary arches allow for a large, open space, opening up to the light. He first used them in Mataró, then in the Palau Güell, in the attic of the Casa Milà and in the Colegio de les Teresianas. Between the arches, there are no beams, just the sill and, in addition, as windows and walls alternate, there are areas of light and shade which give it a compositional quality. Using hyperbolic paraboloids, he tried out what he would design for the Sagrada Família. Parabolic arches are a feature of Gaudí’s work.