The brothers Manuel and Francisco Mateus (Lisbon, 1963 and 1964 respectively) established their firm in 1988 following early collaboration with Gonçalo Byrne, with whom they maintain an open dialogue, sharing his approach and investigation in matters of design. Spatial solutions by Aires Mateus are clear and formally defined, while emphasising resistance and permanence as core qualities of architecture. On the one hand, their work can be read within the larger framework of contemporary Portuguese architecture; on the other, it digs into the conceptual repertoire of archetypical forms. By simplifying and reducing the complexity of the composition in a housing project in Leiria, Portugal (2010), the architects were able to achieve the quintessential dimension of the house. The archetype of the house is a recurring element in their architecture – see the house-shaped entrance to the Université Catholique de Louvain’s Tournai campus (Belgium, 2017). Here, the challenge was to tie together two existing industrial buildings. Aires Mateus graced the existent with the addition of simple but effective scenographic elements. The refined design of their projects is often based on an accurate balance between solids and voids towards an abstraction of the form. This quality is skilfully managed in order to define volumes and composition as shown in the facade for Houses for Elderly People in the tiny village of Alcácer Do Sal, near Lisbon (2010), as well as in a mixed-use building (2008) in Moura, Portugal. In these buildings, the formal definition of the facades is characterised by subtracting volumes from the main form, giving shape to the void. This paradigm of work was illustrated by Aires Mateus in its installation Voids for the 2010 Venice Architecture Biennale, where they illustrated their understanding of space that is a result of “adding subtraction, building excavation”.