Anaximander placed the boundary between Asia and Europe along the Phasis River (the modern Rioni river) in Georgia of 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 BCE.
ˈænɐksˌɪmændɚ plˈeɪst ðə bˈaʊndɚɹi bᵻtwˌiːn ˈeɪʒə ænd jˈʊɹɹəp ɐlˈɔŋ ðə fˈæsiz ɹˈɪvɚ ðə mˈɑːdɚn ɹɪˈoʊni ɹˈɪvɚ ɪn dʒˈɔːɹdʒə ʌv kˈɔːkæsəs fɹʌm ɪts mˈaʊθ baɪ pˈoʊɾi ɔnðə blˈæk sˈiː kˈoʊst, θɹuː ðə sɜːɹˈɑːmi pˈæs ænd ɐlˈɔŋ ðə kjˈʊɹɹɚ ɹˈɪvɚ tə ðə kˈæspiən sˈiː, ɐ kənvˈɛnʃən stˈɪl fˈɑːloʊd baɪ hɪɹˈɑːdəɾəs ɪnðə fˈɪfθ sˈɛntʃɚɹi bˌiːsˌiːˈiː.