The appearance of Tarragona s monumental complex of the Roman amphitheatre changed significantly between 1967 and 1973. Alejandro Ferrant, architect of the Brigadas del PatrimonioArtístico Nacional (Brigades of National Artistic Heritage) of the Spanish government, directed the reconstruction works of an important part of the grandstands, using materials that, over time, have been mimicked/confused with the original structures. The intention seemed to be to restore the original grandeur of the building, although the works focused on the middle sector of the grandstands (media cavea), and only a short section of the upper sector (summa cavea) was reproduced, causing the amphitheatre to be perceived small compared to its original volume. More than 40 years have passed since the works were carried out; the image resulting from Ferrant's intervention is part of city s urban landscape: there are photographs of officialtourist promotion in which almost only the reconstructed parts of the amphitheatre are shown. It is usual that not even the inhabitants of Tarragona know that most of what they see, as well as the seats they use in the events that the building hosts, are a recreation less than half a century old. At a scientific level, Ferrant's interventions are known, but as time goes by it is increasingly difficult to distinguish exactly where they start and end, because constructive techniques were used that, with the patina that gives time, in some areas are visually almost identical to the originals. The examination of the documentation of the archives of the architect, stored and catalogued in the Valencian Library and the delegation of Lleida of the Architects' Association, has allowed us to establish precisely the limits of Ferrant's interventions and provide a detailed chronology of the works.