The sea known as the Pontus is very nearly twenty-two thousand stades in circumference and has two mouths exactly opposite each other, one communicating with the Propontis and the other with the Palus Maeotis, which itself has a circumference of eight thousand stades. As many large rivers from Asia and still more numerous and larger ones from Europe fall into these two basins, the Maeotis being thus replenished flows into the Pontus and the Pontus into the Propontis. The mouth of the Palus Maeotis is called the Cimmerian Bosporus; it is thirty stades in width and sixty in length and is all of no great depth. The mouth of the Pontus is similarly called the Thracian Bosporus and is a hundred and twenty stades long and not of the same width throughout. From the side of the Propontis its beginning is the passage between Calchedon and Byzantium which is fourteen stades in width. On the side of the Pontus it begins at the so-called Holy Place, where they say that Jason on his voyage back from Colchis first sacrificed to the twelve gods.
This lies in Asia and is about twelve stades distant from the opposite point in Thrace the temple of Sarapis. There are two causes of the constant flow from the Palus Maeotis and the Pontus, one, at once evident to all, being that where many streams fall into basins of limited circumference the water constantly increases and, if there were no outlets, would continue to mount higher and occupy a larger area of the basin. In the case, however, of there being outlets the surplus water runs off by these channels. The second cause is that as the rivers carry down into these basins after heavy rains quantities of all kinds of alluvial matter, the water in the seas is forcibly displaced by the banks thus formed and continues to mount and flow out in like manner through the existing outlets. As the influx and deposit of alluvium by the rivers is constant, the outflow through the mouths must likewise be constant.
The true reasons then of the current flowing from the Pontus are these, depending as they do not on the reports of traders but on reasoning from the facts of nature, a more accurate method than which it is not easy to find.
But since our attention is now fixed on this subject, I must leave no point unelaborated and barely stated, as is the habit of most writers, but must rather give a description of the facts supported by proofs, so that no doubts may be left in the reader’s mind. For this is the characteristic of the present age, in which, all parts of the world being accessible by land or sea, it is no longer proper to cite the testimony of poets and mythographers regarding matters of which we are ignorant, “offering”, as Heraclitus says, “untrustworthy sureties for disputed facts”, but we should aim at laying before our readers a narrative resting on its own credit.
I say then that the silting up of the Pontus has gone on from time immemorial and still continues, and that in course of time both this sea and the Palus Maeotis will be entirely filled, if the existing local conditions remain the same and the causes of the alluvial deposit continue to act. For time being infinite, and the area of these basins being certainly limited, it is evident that even if the accretions were quite insignificant, the seas will be filled up in time; for by the law of nature if a finite quantity continually grows or decreases in infinite time, even if the increase or decrease be infinitesimal — for this is what I now assume it stands to reason that the process must finally be completed. But when, as in this case, the increase is no small one, but a very large quantity of soil is being deposited, it is evident that what I state will not happen at some remote date, but very shortly. And it is indeed visibly happening. As for the Palus Maeotis it is already silted up, the greater part of it varying in depth between five and seven fathoms, so that large ships can no longer navigate it without a pilot. And while it was once, as all ancient authorities agree, a sea continuous with the Pontus, it is now a fresh-water lake, the salt water having being forced out by the deposits and the inflow from the rivers prevailing.
Some day it will be the same with the Pontus; in fact the thing is actually taking place, and although not very generally noticed owing to the large size of the basin, it is apparent to anyone who gives some slight attention to the matter.
For the Danube flowing from Europe and falling into the Pontus by several mouths, a bank formed of the matter discharged from these mouths and reaching out to sea for a day’s journey, stretches for about a hundred miles opposite them, and ships navigating the Pontus, while still far out at sea, often at night when sailing unwarily run aground on certain parts of this belt, which are known to sailors as “The Paps”. The reason why the deposit is not formed close to the land but is projected so far we must consider to be as follows. As far as the currents of the rivers prevail owing to their strength and force a way through the sea, the earth and all other matter carried down by the stream must continue to be pushed forward and not suffered to rest or subside at all; but when owing to the increasing depth and volume of the sea the rivers lose their force, then of course the earth sinks by its natural weight and settles. This is why in the case of large and swift rivers the deposits are formed at a distance, the sea near the coast being deep, but in that of small and sluggish streams the sand-banks are close to their mouths. This becomes especially evident during heavy rains; for then insignificant streams when they have overpowered the surge at their mouths push forward their mud out to sea for a distance exactly proportionate to the force of their currents. We must not at all refuse to believe in the extent of the bank at the mouth of the Danube and in the quantity of stones, timber, and earth carried down by the rivers in general. It would be folly to do so when we often see with our own eyes an insignificant torrent scooping out a bed and forcing its way through high ground, carrying down every kind of wrood, stones, and earth and forming such vast deposits that the spot may in a short space of time be so changed in aspect as to be unrecognizable.
We should not therefore be surprised if such great rivers flowing continuously produce some such effect as I have stated, and finally fill up the Pontus; we must indeed anticipate this not as a probability but as a certainty if we reason rightly. The following is an indication of what may be expected. The Palus Maeotis is at present less salt than the Pontus, and we find that the Pontus correspondingly is decidedly less salt than the Mediterranean. From which it is evident that when a period has elapsed which stands to the time it takes to fill up the Palus Maeotis in the same proportion as the cubic capacity of the larger basin to that of the smaller, the Pontus will become, like the Palus Maeotis, a shallow fresh-water lake. We must indeed anticipate this result still earlier, since the rivers that fall into the Pontus are larger and more numerous.
What I have said may suffice to satisfy the doubts of those who are unwilling to believe that the Pontus is filling up and will be filled up, and that so large a sea will be converted into a shallow lake. But I speak especially in view of the falsehoods and sensational tales of seafarers, so that we may not be obliged owing to ignorance to listen greedily like children to anything that is told us, but having now some traces of the truth in our minds may be more or less able to form an independent judgement as to the truth or falsehood of the reports made by this or that person.
I must now resume my account of the specially favourable situation of Byzantium. The channel connecting the Pontus and the Propontis being a hundred and twenty stades in length, as I just said, the Holy Place marking its termination towards the Pontus and the strait of Byzantium that towards the Propontis, half way between these on the European side stands the Hermaeum on a promontory running out into the channel at a distance of about five stades from Asia and situated at the narrowest part of the whole. It is here, they say, that Darius bridged the straits when he crossed to attack the Scythians. Now the force of the current from the Pontus has been so far uniform owing to the similarity of the country on each bank of the channel, but when it reaches the Hermaeum on the European side, which is, as I said, the narrowest point, this current from the Pontus being confined and sweeping strongly against the headland, rebounds as if from a blow, and dashes against the opposite coast of Asia. It now again recoils from this coast and is carried against the promontory on the European bank known as the Hearths, from which its force is once more deflected to the place on the Asiatic bank called the Cow, where legend says that lo first found a footing after crossing. Finally the current runs rapidly from the Cow to Byzantium itself, and dividing into two near the city, sends off its smaller branch into the gulf known as the Horn, while the larger branch is again deflected. It has however, no longer sufficient force to reach the coast opposite, on which stands Calchedon; for as it has now several times crossed and recrossed the channel, which here is already of considerable width, the current has now become feebler, and ceases to make short rebounds to the opposite coast at an acute angle, but is rather deflected at an obtuse angle. It therefore fails to reach Calchedon and flows out through the strait.
What therefore makes the situation of Byzantium so favourable and that of Calchedon the reverse is the fact here stated. To look at them indeed you would say they were equally well placed, but nevertheless it is not easy to reach Calchedon by sea, if one wishes, while to Byzantium the current carries one whether one wishes or not, as I just said. Evidence of this is that those who wish to cross from Calchedon to Byzantium cannot sail in a straight course owing to the current between, but steer obliquely for the Cow and the place called Chrysopolis which the Athenians once occupied by the advice of Alcibiades and used it when they first attempted to levy toll on vessels bound for the Pontus and from hence commit themselves to the current which perforce carries them to Byzantium. The approaches by sea to Byzantium from the other side are equally favourable. For those sailing with a south wind from the Hellespont, or from the Pontus to the Hellespont with the Etesian winds, find the course from Byzantium along the European coast to the commencement of the narrows at Sestus and Abydus a straight and easy one, and so is the return voyage to Byzantium. But the voyage from Calchedon along the Asiatic coast is the reverse of this, because one must follow the shores of a deep gulf, and the headland formed by the territory of Cyzicus runs out to a great distance. Nor can ships sailing from the Hellespont to Calchedon easily coast along Europe and then on approaching Byzantium turn and make for Calchedon, as the current and the circumstances mentioned above make it difficult. And similarly it is quite impossible for a ship leaving Calchedon to make the coast of Thrace at once owing to the current between, and owing to the wind. Both the south and north winds are adverse to both the attempts, since the south wind will carry one towards the Pontus and the north wind away from it, and these are the winds one must avail oneself of for the voyage from Calchedon to Hellespont or for the voyage back.
Such are the causes of the favourable position of Byzantium as regards the sea.
(Source: Polybius, The Histories, Vol.II, Book IV, Loeb Classical Library)
Research-Selection for NovoScriptorium: Anastasius Philoponus