 Anaximander placed the boundary between Asia and Europe along the Phasis River (the modern Rioni) in the Caucasus (from its mouth by Poti on the Black Sea coast, through the Surami Pass and along the Kura River to the Caspian Sea), a convention still followed by Herodotus in the 5th century BC.As geographic knowledge of the Greeks increased during the Hellenistic period, this archaic convention was revised, and the boundary between Europe and Asia was now considered to be the Tanais (the modern Don River).This is the convention used by Roman era authors such as Posidonius, Strabo and Ptolemy.