I have long been interested in the origin of the idea that the world is divided into separate continents, having co-written a book on the topic in 1997. While currently working on the Black Sea region, I have been reminded of how central the Black Sea was to the original continental scheme.
The (known) world was first divided into two continents – Europe and Asia – by Greek thinkers located in the city of Miletus in what is now western Turkey. In the 6th century BCE, Miletus was one of the largest and wealthiest Greek city states. It is also commonly regarded as the birthplace of Greek science and philosophy, being the home of the so-called Ionian Enlightenment of the same century. Beginning in the 8th century BCE, Miletus, like many other Greek city states, established numerous colonies, most of which were located around the Black Sea. Milesian navigators and merchants had extensive experience in this water body, and early Milesian thinkers relied on their knowledge when mapping the world.
According to traditional sources, the first Greek world map was made by Anaximander of Miletus. It was subsequently revised by Hecataeus, a noted geographer of the same city. Neither map survived, but they have been reconstructed based on surviving descriptions. As these reconstructions show, the term “Europe” was used to designate the large landmass located to the left as Milesian navigators moved between islands and through narrow passages as they voyaged from their home city across the Black Sea, whereas “Asia” referred to those lands on the right. As the Milesians were also familiar with the Mediterranean, these same terms were used, respectively, for the landmasses to the north and south of this sea (“Asia” was not generally differentiated on continental grounds from “Libya” [or Africa] by Milesian geographers).
In world vision of these early geographers, the division between Asia and Europe in the extreme east continued along the Phasis River (source of the word “pheasant”), now known as the Rioni River of western Georgia. This river was not well understood and was evidently believed by some to link the Black Sea to the eastern reaches of the encircling Ocean. Later Greek thinkers of the fifth and fourth centuries BCE generally regard their own realm as being strung along a series of waterways that extended from the Strait of Gibraltar to what is now western Georgia. As Plato ostensibly quoted Socrates, “I believe that the earth is very large and that we who dwell between the Pillars of Hercules and the river Phasis live in a small part of it about the sea, like ants or frogs about a pond” (Phaedo, 109a). With the world conceptualized in such a manner, it made sense to distinguish the northern side of this division as one land mass, Europe, and the other side as another, conceptualized either as either Asia or as Asia and Libya (Africa).
Later Greek and Roman geographers revised the continental schema, moving the division between Europe and Asia from the Phasis River (Rioni) to the Tanais (Don) River. This maneuver highlighted the passage into yet another enclosed sea (the Sea of Azov, then known as Lake Maeotis), through yet another narrow passage, the Strait of Kerch (then known as the Cimmerian Bosporus). A reconstruction of a Roman world map nicely shows the resulting threefold division of the world, with Europe almost separated from Asia by a north-south-running series of waterways beginning in the Aegean Sea and ending in the Sea of Azov, and Asia almost separated from Africa by the Red Sea (labeled as the Arabian Sea on this map.) This model of the world would become the foundation for all later continental divisions.