The article deals with some problems connected with the development of Boristhenes and Olbia during the colonization period. Analysing old and recent archaeological data obtained in Olbia, the author makes an attempt to review the generally accepted chronology. Remains of buildings connected with dwelling, economical activities and cult prove that Olbia was founded in the second quarter of the 6th с. ВС. This means that the development of agricultural area, whose early period is traditionally connected with Boristhenes and the later one with the latter, can be connected only with Olbia, for the earliest settlements were contemporary with this city. The origin of Olbia corresponds chronologically to the establishment of the polis cult of Apollo the Healer (A.S. Rusyayeva), to the coin-like arrow-shaped metal pieces related to it by their se-mantics (V.A. Anokhin), and a system of extra-urban sanctuaries marking the borders of the Ol-bian chora (S.B. Buiskikh). A free area reserved in the centre of Olbia which was used for the agora in the early 5th с. ВС, is another fact that makes it possible to maintain that Olbia had been originally conceived as a polis centre. Commercially oriented Boristhenes, which did not have its own chora, should be regarded as an emporium depending first on Miletus, and after the foundation of Olbia on the Olbian polis. This thesis is in the line of L.V. Kopeikina's and Yu.G. Vinogradov's ideas. The dynamics of dwelling-houses and cult buildings shows that Boristhenes and Olbia were developing as city centres.