Abstract This article is devoted to the urban space of Pontic Olbia – to the growth of its territory, and the emergence of its early defensive system consisting of earthworks with moats, which had surrounded the city as early as the Late Archaic period. Conclusions are drawn about the role of the settlement structure in the western part of the city, which had earlier been interpreted as Herodotus’ proasteion, but which – in the light of discoveries made by a Ukrainian-German research project – has been recognised as an integral part of the city. The chronology of the mud-brick and stone fortifications erected no later than in the middle of the 4th century BC, before Olbia was besieged by Zopyrion in 331 BC, has been amended. This work has made it possible to propose a new diagram for Olbia’s spatial development in the Late Archaic and Classical periods.