The Symplegades or ‘Clashing Rocks’, situated at the Bosporus, are known in Greek mythology as one of the challenges encountered by Jason and the Argonauts. Pindar describes Jason’s journey to the ‘Inhospitable Sea’ (Black Sea) via the Clashing Rocks [1787.61].
Rosario Vieni has suggested that the Symplegades, were precursors of the Pillars of Heracles, John Lundwall in Mythos and Cosmos [1747.305-6] also suggests a linkage between the Symplegades and the Pillars of Herakles!(a)
(a) https://www.quora.com/Where-are-the-pillars-of-Hercules (just over halfway down the page)
The River Danube is the second-longest river in Europe, which was known to the ancient Greeks as ‘Istros’. It rises in Germany’s Black Forest and after passing through many countries, including four capital cities, it eventually empties into the Black Sea.
A number of researchers have associated the river with Plato’s Atlantis. One of the earliest was Nicolae Densusianu who proposed that Atlantis had been situated in ancient Dacia, his native Romania. Over a century later some of his ideas have been revived by other Romanian commentators such as Adrian Bucurescu and Alexandra Furdui, who also translated Densusianu’s monumental work into English.
Densusian’s nationalism is now frowned upon and there is an understandable suspicion that his modern Romanian supporters may have similar underlying motivations.
There is a gorge on the Danube known as the Iron Gates which provides part of the boundary between Serbia and Romania. Densusianu located the Pillars of Heracles at the Iron Gates, an idea supported by Ticleanu, Constantin & Nicolescu at the 2008 Atlantis Conference, who place Atlantis further west on the Pannonian Plain [750.365]. In 2020, Veljko Milkovic also placed the ‘Pillars’ at the Iron Gates on the Danube and Atlantis in the Pannonian Basin(c) in his book Panonska Atlantida .
However, Ranko Jakovlievic expressed the view that the Iron Gates section of the Danube was the location of Atlantis!
Related to this, is the claim by an anonymous ‘Sherlock’ that Pindar’s Olympian Ode 3 suggested that the Pillars of Herakles had been situated at the confluence of the Seva and Danube rivers near modern Belgrade(b).
A recent book  by Antonije Shkokljev & Slave Nikolovski–Katin also recount an ancient version of the ‘Labours of Hercules’ that took place in the Balkans.
Christian and Siegfried Schoppe locate Atlantis east of the Danube Delta on Snake Island (Zimiinyi) in the Black Sea, an idea now adopted by George K. Weller(a). [Zimiinyi, Ukrainian territory, was occupied by the Russians 25.02.22 as part of their invasion of Ukraine]
Pindar (522-443 BC) was one of the nine ancient Greek lyric poets. He refers to the ‘Pillars of Heracles’ in three of his victory odes, Olympian 3.43-45, Nemean 3.19-23 and Isthmian 4.11-13, doing so in a manner which indicates that the term was used as a metaphor for the limit of human (Greek) experience. As such, the location of the Pillars would have changed as the colonial and commercial expansion of the Greeks developed beyond the Aegean.
>One commentator has interpreted Pindar’s Olympian Ode 3 as referring to the Pillars of Herakles being placed at the ‘Springs of Ister’ on the Danube near Belgrade, noting that “this is the very edge of Pindar’s Celtic world and a point beyond which a Greek probably did not want to venture.“(b)<
Oliver D.Smith has drawn attention to the Nemean Ode 4, 65-70 as having echoes of Plato’s description in it(a).
(a) https://atlantisresearch.wordpress.com/ (now offline)
The Black Sea was known to the Greeks as the Euxine Sea and according to Strabo (1.2.10), in antiquity was often simply referred to as “the sea” (pontos). It has also been known as the Scythian Sea after the people who lived on its northern shore. Pindar referred to it as the ‘Inhospitable Sea’.
It received little attention in connection with the Atlantis mystery until the 19th century when two French writers, André de Paniagua and Moreau de Jonnès, independently located Atlantis in the Sea of Azov. Some years later in 1923, R.A. Fessenden, a Canadian professor of Mathematics and Electrical Engineering wrote about the prehistoric flooding of a civilisation in the Caucasus region, which he linked with Plato’s Atlantis. The text of this extensive work is now available on the Internet(a).
Trevor Palmer has written a useful paper (2009) on the Black Sea and the gradual development of theories relating to its dramatic connection with the Mediterranean and how it may have influenced the mythologies of the Middle East and possibly further afield.
Palmer concluded that “The various groups currently investigating the area are agreed that cataclysmic flooding took place during the Late Pleistocene, but remain divided about whether similar floods also occurred during the Holocene. Eye-witness accounts of catastrophic floods in the Black Sea basin at either time could have been passed on to future generations, eventually giving rise to the later Mesopotamian legend of Uta-napishtim and, subsequently, the Biblical story of Noah. However, in the absence of any direct evidence of cultural transmission, that can presently only be regarded as plausible speculation.”(p)
Little was heard of the region again until 1998 when Ryan & Pitman identified the flooding of the Black Sea with Noah’s Flood. This was followed in 2001 by Ian Wilson‘s Before the Flood , which reflected a similar line of thought.
In 2004, the Bulgarian father and son oceanographers, Petko and Dimitar Dimitrov published their book, The Black Sea, the Flood and the Ancient Myths, in English, which supported much of Ryan and Pitman’s work. Unlike them, who based much of their conclusions on a study of molluscs, the Dimitrovs focused on sedimentation evidence. Their book is now available, in English, as a free pdf file(d). They also suggest that this Holocene influx into the Black Sea also triggered the Vedic Aryan migration to India(g).
Ryan and Pitman’s book unintentionally triggered the imaginations of a number of people into considering the possibility of a possible link between this inundation and the sinking of Atlantis. While Ryan and Pitman have made no such suggestion, others such as Ian Wilson have seen a distorted memory of the event as a possible inspiration for Plato’s story. In 2009, Liviu Giosan, a geologist at the Woods Hole Oceanographic Institute published a paper(e) which suggested that prior to the intrusion of the Mediterranean, the level of the Black Sea had been just 30 metres below its present level rather than the 80 metres proposed by Ryan and Pitman. This would imply a less extensive degree of flooding than previously thought. Giosan has offered a sceptical Ryan an opportunity to replicate his tests.
Although the scenario pictured by Ryan & Pitman and others is of very rapid flooding of the original smaller Black Sea, more recent studies appear to indicate a more gradual rising of the water levels. “With more data to be analysed, it supports the idea that the waters rose unnoticeably, by metres over centuries, even millennia.”(o)
Nick Thom, a British engineer, wrote The Great Flood  which includes a section on the Black Sea in which he suggests that the flow of water was from the Black Sea into the Sea of Marmara rather than the other way around.
Nearly two hundred years ago Josiah Priest in his 1835 book American Antiquities  also offered evidence from Euclid of Megara that the flow of water had been from the Black Sea to the Aegean. Apparently, Euclid heard this from Anacharsis a philosopher from the northern coast of the Black Sea related how the inflow from the rivers of Europe and Asia raised the level of the ‘Sea’ until it breached the landbridge and spilled over into the Sea of Marmara.
>Paul Dunbavin has entered the Black Sea flood(s) debate with a 2020 paper entitled Diodorus Siculus and the Black Sea Flood(q). This lengthy essay covers a lot of ground, in particular the comments of Diodorus Siculus who described a Samothracian flood story that appears to contradict the flood described by Ryan & Pitman as it describes a flow of water in the opposite direction. Consequently, the evidence offered by Diodorus is often discounted as ‘unreliable’. Dunbavin, however, offers a possible solution with the suggestion that “The Samothracian flood, as described by Diodorus, could only have occurred after the Black Sea Flood.”<
More recently, Christian & Siegfried Schoppe, two German researchers have also asserted that the Black Sea was the original ‘Atlantis Ocean and that Atlantis was located in that region . They have suggested that Snake Island located east of the mouth of the Danube was the probable site of Plato’s city. Their contention is that around 5500 BC a landbridge at the Bosporus was breached causing extensive flooding that created what we now know as the Black Sea. Until that time there had only been a small freshwater lake in the region. Although their book was published in German, the Schoppes have a website(b) with a useful amount of English content.
The somewhat eccentric duo of the late Flying Eagle (1920-2007) and Whispering Wind, who also advocated a Black Sea location for Atlantis(a)(f), claimed a specific site on the Strait of Kerch between the Black Sea and the Sea of Azov. Their theory was first expounded in their book  in 2004. They also followed the Ryan and Pitman date of 5500 BC for the inundation of the Black Sea.
The evidence to date suggests that the flooding of the Black Sea coincided with a storegga event, which would require a catastrophe on a scale not previously considered. In a 2017 paper(i), John M. Jensen offers a range of evidence to support this contention.
A rather different approach is taken by the German researcher Werner E. Friedrich, who pushes back the expansion and the raising of the level of the Black Sea to around 10000 BC, at the end of the last Ice Age. He believes that this led to the flooding of Atlantis, which he claims to have been situated on a plain that had lain between ancient extensions of the rivers Donau and Don. Friedrich located the Pillars of Heracles in the Sea of Marmara[p.39].
A.I. Zolotukhin places Atlantis in western Crimea on his multilingual website with the inviting title of Homer and Atlantis(j).
The legendary destroyed city of Ancomah is frequently compared to Plato’s description of the destruction of Atlantis. It was reputed to have existed in the vicinity of the ancient port city of Trabzon, which is located on the southeast coast of the Black Sea.
The concept of a Black Sea Atlantis has the support of the rather eccentric Church of Vrilology(h)!
In October 2018, an attempt was made to breathe new life into the idea of Crimea as a remnant of an Atlantis submerged under the Black Sea. Unfortunately, it offers no evidence or references in the badly translated article(k). In the same month, it was reported that the oldest intact shipwreck was discovered in the Black Sea by an Anglo-Bulgarian team. It was identified as a Greek trading vessel dated to 400 BC(l). The oxygen-free waters at the bottom of the Black Sea had preserved it and dozens of others located by the team.
In early 2019, George K. Weller, building on the theories of the Schoppes, also proposed the Black Sea as Atlantis’ home, again nominating Snake Island as the home of Mr. and Mrs. Poseidon, which, before the Black Sea was flooded, would have been the central peak of their island home, as referred to by Plato(n).
One of the most comprehensive internet papers on all aspects of the history of the Black Sea can be found on the Encyclopaedia Iranica website(m).
(k) https://ktelegram.com/scientists-crimea-may-be-a-fragment-of-the-lost-city-of-atlantis/43728/ (link broken Jan. 2019)