The Collegial Temple of the Fabri Navales (or Shipbuilders) is located on the northern flank of the western part of Ostia’s Decumanus Maximus and was uncovered during the major excavations of 1938-39. This study presents and analyses the results of the excavations carried out on this site between 1992 and 2005 by the Université Saint Louis in Brussels and the Université de Namur, in cooperation with the Superintendence of Ostia – now Archaeological Park of Ostia antica. Built in the last decade of the 2nd century BC, under Commodus and Septimius Severus, this Temple comprises tabernae on the façade, a vast courtyard with porticoes preceded by a large covered hall and a high podium in antis. The site, abandoned in the 5th century, was home to a large marble deposit. New research revealed the existence of a vast fullonica under the ruins of the Temple, buried beneath a high fill. The layout of this fuller’s workshop, built under Trajan and remodelled several times during the 2nd century, was remarkably organised around four large basins flanked by numerous fulling stalls occupying the entire rear part of the plot, while a courtyard flanked by shops completed its extension to the front of the site. Archaeological surveys carried out under the clay floors of these tabernae, built before the middle of the 1st century AD, have revealed the earliest levels of occupation of the plot, revealing the existence of an even older courtyard and hydraulic structures – a well and a reservoir (castellum aquae) – dating back to the 1st century AD. These discoveries reopen the debate on the evolution of water distribution in this part of the city, from the late-Republican period to the end of the 2nd century AD. A study of the long development of this plot confirms the use of all the buildings occupying this block (R III,II), which until the Late Empire was entirely devoted to different activities, always linked to crafts and trade.