On 1988 a frightful fire broke out in Chiado, destroying 18 buildings, of which most part only the facades remained. A reconstruction plan was committed to Álvaro Siza, who fulfilled the request to preserve the existing buildings. The bibliography is mainly devoted to historical events, and architectural design options. There are few publications on the constructive and structural interventions, the objective of this study, to allow a broader knowledge about the intervention at various levels and disciplines. This is of particular interest in the scope of the research project “Siza Atlas. Filling the gaps for World Heritage” which aims to contribute to the nomination of a group of Siza's works for the World Heritage List. The subject is analyzed trough complementary readings: research of bibliography, documentation from the archive and in situ observations. A comparative analysis of the interventions proves a common method of construction with reinforced concrete structure built in situ. The principal improvement of the plan concerned the public space, recreating paths between the blocks, connecting the lower and upper levels of Chiado.info:eu-repo/semantics/publishedVersio