Book 6 discusses the portion of the continent of Asia that had not been examined in Book 5, beginning at the Thracian Bosporus, where Book 5 ended (5.151). Now Pliny continued from the Bosporus around the Asian shore of the Pontus Euxinus, or Black Sea (1–24), with some diversion into the interior of Asia Minor. He then moved into Armenia and the Caucasus (25–35) and the Caspian region (36–49). After a consideration of the extreme north and east of the known world (50–5), the Natural History focused on India, Taprobane, and Ariana (56–106). Returning west, the account moves into the Persian plateau and Mesopotamia (107–141), and then the part of Arabia not previously discussed (142–77), followed by Aethiopia (178–97), and concluding with various islands (198–205). The final portion of the geographical books of the Natural History is about terrestrial parallels (206–20).