The main area of this study is the city centre with a focal point on the Forum’s area. Until now, it has not been possible to study the Forum as a coherent unit considered as in a diachronic perspective. Recent research conducted by the Berlin-Kent-Ostia Excavations, Humboldt-Ostia-Forum Project and Ostia-Forum-Project in the period between 2008 and 2019 have provided evidence of the development of the Forum. The research has been conducted through excavations, photogrammetry and geophysical analyses. Before these comprehensive analyses, excavations have never been conducted in the Forum’s area since the rigorous excavations in the first half of the 20th century. It is therefore, for the first time, possible to analyse, contextualise and trace several different orientation and planning symmetries of different building layouts in the attempt to interpret the genesis of the different forum-layouts.