Written by Graham | Created: Monday 26th August 2019 @ 1220hrs | Revised: Tuesday 29th September 2020 @ 2345hrs; Friday 18th December 2020 @ 1017hrs
Plato's description of a shallow Atlantic, which he explains as the result of the sinking of the island, has a number of precursors and successors in ancient literature. Plato is, however, unique among extant sources in that he is the only one to proffer a potential explanation for the source of these shallows. It is this suggestion, developed rationally, which made his suggestion of a major sunken island off the western side of Europe and Africa compelling to later thinkers.
Soon after Plato, his one-time student Aristotle [Meteorology 2.1] would write: -
Outside the pillars of Heracles the sea is shallow owing to the mud, but calm, for it lies in a hollow.
Herodotus notes three attempts to circumnavigate the continent. A Phoenician expedition chartered by Necho of Egypt [4.42] was apparently successful, but the other two - that of "Sesostris" [2.102] and Sataspes on the orders of Xerxes [4.43] - both failed, with the reasons given being the impassability of the sea.
First, Sesostris, a composite figure whose manifold accomplishments seem to be based on any number of successful pharaohs of the Middle and New Kingdoms. He: -
[...] proceeded in a fleet of ships of war from the Arabian gulf along the shores of the Erythraean sea, subduing the nations as he went, until he finally reached a sea which could not be navigated by reason of the shoals.
It is likely that this expedition never made it into the west: Pliny the Elder [6.36], citing Ephorus, notes the existence of small islands: "Ephorus states that those who sail from the Red Sea into the Æthiopian Ocean cannot get beyond the Columnæ there, some little islands so called."
Sataspes meanwhile claims that he got as far as the land of a "dwarfish race, who wore a dress made from the palm-tree," thought could get no further "because the ship stopped, and would not go any further." Xerxes is unamused and has Sataspes impaled for failing to carry out his orders. The "dwarfish race" are presumably identical to that encountered by the Nasamoneans at the apogee of their overland expedition into West Africa [2.32]: -
After journeying for many days [from east to west] over a wide extent of sand, they came [...] to a plain where they observed trees growing; approaching them, and seeing fruit on them, they proceeded to gather it. When they were thus engaged, there came upon them some dwarfish men, under the middle height, who seized them and carried them off. [...] They were led across extensive marshes, and finally came to a town, where all the men were of the height of their conductors, and black-complexioned. A great river flowed by the town, running from west to east, and containing crocodiles. [...] Etearchus [...] declared that the Nasamonians got safe back to their country, and that the men whose city they had reached were a nation of sorcerers.
This information is couched in terms of a conversation between a group of Cyrenaeans and Etearchus, the king of the Ammonians, at the oracle of Siwa, where the source of the Nile was discussed. Etearchus believes that the river in the account is a western branch of the great river, answerable to what the Greeks believed about the Danube having a mouth in Istria and a concept which appears as late as Muhammad al-Idrisi. Though this speculation has little bearing on reality (Rawlinson suspects that the passage contains a reference to the Niger) or, on the face of it, the subject at hand, it was off this coast that Sataspes claimed his fleet found themselves unable to proceed. It was also in this general region that the Carthaginian admiral Hanno was forced to turn back, though, in his case, this was due to lack of provisions.
As a result of these and other accounts, Strabo, summarising previous efforts to sail around Africa, makes the following observation: -
[A]ll those who have made coasting-voyages on the ocean along the shores of Libya, whether they started from the Red Sea or from the Pillars of Heracles, always turned back, after they had advanced a certain distance, because they were hindered by many perplexing circumstances, and consequently they left in the minds of most people the conviction that the intervening space was blocked by an isthmus; and yet the whole Atlantic Ocean is one unbroken body of water, and this is particularly true of the Southern Atlantic. All those voyagers have spoken of the last districts to which they came in their voyagings as Ethiopic territory and have so reported them.
Strabo, who is discussing Homer's sundered Ethiopians [Odyssey 1.22-24], dismisses the existence of an isthmus as a potential solution, and instead suspects that all countries bordering the southernmost reaches of the ocean were anciently termed Ethiopia [1.2.27]. The southerly location for the blockages also contrasts with a notice in Aristotle's Meteorology [2.1], which states that the northern seas are shallower than those of the south: -
[T]he greatest volume of water flows from the higher regions in the north. Their alluvium makes the northern seas shallow, while the outer seas are deeper.
Writing in the same century as Herodotus, Pindar places "the streams of the shallows" and "monstrous beasts in the sea" beyond the Pillars of Heracles [Nemean 3:20-26], whilst Euripides [Hippolytus 742-727] also attests to the western ocean being blocked: -
How I wish I could fly to that shore where the apple trees grow.
The trees of the harmony lovers, the Hesperides!
There, where Poseidon, the Lord of the sea, forbids the mariners from passing through into the turbulent waters and where he marks the boundary in the sky which Atlas holds.
The origins of Plato's description of the sea which cannot be passed by ship is perhaps the Phoenician Himilco. The account of Himilco's voyage appears in the work of Avienus [114-129; 380-389; 404-415], and describes Himilco's successful attempt to garner ties in north-western Europe being hampered by a variety of factors: the sea has many sandbars [125-126], seaweed  and sea monsters [128-129], and there are long periods with no wind , and vast amounts of fog [380-389]. Of these, seaweed and sea monsters are features which recur elsewhere, and the sandbars evoke Plato's shoals [Tim. 25d; Crit. 108e-109a].
A likely solution which has been proposed is that the dangers present in the Atlantic were talked up or invented by the Carthaginians as a means to deter Greek exploration, though the influence of and need for such propaganda may be exaggerated, and ignores areas where the dangers listed were indeed present. Nevertheless, Strabo [3.5.11] does record an incident postdating Plato in which a Phoenician captain deliberately beached his ship, causing his Roman pursuers to run aground.
Duane Roller notes that: "[i]t is more probable that [Himilco] came to the area four days beyond the Pillars of Herakles used by the fishermen of Gades, a place thick with seaweed that appeared when the tide was low - hence a coastal location - and where tuna of unusual size were caught and send to Carthage." Further to the south, Marijean Eichel and Joan Markley Todd note an interesting phenomenon mentioned in the Africa Pilot: -
The Africa Pilot reports that north and south of Cape Nun there is an interesting phenomenon, apparently caused by the immense volume of fine sand blown off the desert: "For some distance both north and south of Cape Nun, as well as to seaward, the water has a red tinge, with a thick muddy appearance, so that the track of a vessel is visible for some time."
Though they concede that this could "be a modern phenomenon, due to the accelerated drying-up of the Sahara in modern times, there is no doubt that the same strange juxtaposition of desert and fog existed then as now." Such a phenomenon, if present during the Classical age of the Greeks, could provide an alternative explanation of the sea of mud mentioned by Plato.