The problem of the foundation of Tanais still remains disputable. Archaeological data allows to assume, that the population of Tanais in the 3rd-lst centuries BC was heterogeneous. The population of Tanais.' included inhabitants of the Greek quarter, which existed in the territory of Scythian Elizavetovka settlement in the second half of 4th c. BC. Those Greeks might have been political emigrants from Bosporus. The population of Tanais also included representatives of the barbarian population of the Low Don area, and among them the barbarians from Elizavetovka settlement. Probably, Tanais was founded at the end of 4th - beginning of the 3rd c. BC. In the 260s BC the population of Tanais was augmented by the inhabitants of Bosporan Greek colony at Elizavetovka. The authors suppose that this colony might be identified as Alopekia mentioned by Strabo and Ptolemy. The major factor which influenced the foundation of Tanais was the political situation in the Low Don area and in the neighboring regions about the late 4th - early 3rd century BC. Destruction of the Ataios' «state» and disintegration of Sauromatian tribal alliance had led both to the growth of Bosporus' political activity and activation of new tribes - Sirmatians and Sarmatians of the ancient written tradition. In these conditions unfortified and small Tanais, probably, had been supported by the Sirmatians and Sarmatians. Without this support Bosporus rapidly lost its influence in the region and its trading colony - Alopekia. These circumstances had caused political independence of Tanais and made it, in particular, politically independent of Bosporus in the 3rd-1st centuries BC.