The study of the so-called Magazzini Traianei di Portus was part of a wide-ranging International research project dedicated to “Warehouses and storage structures in the ancient Greco-Roman world”. Multidisciplinary campaigns took place between 2009 and 2015 (archaeology of construction, excavation, geo-archaeology, anthropology, numismatics, ceramics etc.). The results have been partially published in various contributions by specialists and will shortly be published together as a monograph for the Collection de l'École française de Rome. The warehouse complex covers an area of 8 hectares (c. 300 x 2790 m) and was formed by two twin buildings. While the north building was built around the port’s ancient wet dock, the southern one was built around a large open space, traditionally and erroneously identified as the Foro Olitorio. The careful design presented a plan arranged symmetrically with respect to the central axis formed by the so-called Colonnaded Road. A double series of cells closed the structure on the west side, along the so-called Portico of Claudius, which constituted the seaward and monumental facade of the complex. The structure originally foresaw c. 410 storerooms of c. 90 m2 each, corresponding with an effective capacity of almost four hectares. In the three east-west structures, there were passageways and ramps every 4-6 cells, which allowed north-south circulation and access to the upper floors. The original project did not foresee upper floors on the west side; the ramps visible today belong to the restructuring of the warehouse’s facade in the Antonine period. The investigations provided a precise chronology for the building and identified the main construction phases. The Claudian date for the design of the complex and construction of the imposing _opus_ _reticulatum_ foundations. In the same period, the monumentalisation began that was neglected during the following era, during which attention focused on perfecting the functional aspects. There was little evidence to suggest that the storage cells were completed during the original phase, for which only scarce interventions in the northern part of the warehouse were identified. The first substantial modifications to the original layout date to the Antonine period during which, in addition to the completion of the storage cells, a number of ramps were built on the west side of the monument. The Severan period saw significant remodelling of the structure with the reconstruction of a part of the cells, the blocking of the spaces between the columns to increase the storage space, in addition to the installation of a new system of docks to unload the cargoes outside the by then closed-off area of the warehouse. Among the more interesting aspects regarding the construction of this ambitious project is the almost systematic presence of raised floor, which suggests, with some certainty that the warehouse could hold any type of merchandise, even delicate the most delicate such as grain. Confirmation is provided by other features put into place to guarantee good micro-climatic conditions inside the cells, such as the airtight facings on the walls (_opus_ _signinum_), the substantial thickness of the walls (c. 90 cm), the significant width of the entrances and the counter positioning of the windows to ensure good air circulation in the spaces.