37. Eratosthenes599 cannot, therefore, be found fault with on these grounds; what may be objected against him is as follows. When you wish to give a general outline of size and configuration, you should devise for yourself some rule which may be adhered to more or less. After having laid down that the breadth of the space occupied by the mountains which run in a direction due east, as well as by the sea which reaches to the Pillars of Hercules, is 3000 stadia, would you pretend to estimate different lines, which you may draw within the breadth of that space, as one and the same line? We should be more willing to grant you the power of doing so with respect to the lines which run parallel to that space than with those which fall upon it; and among these latter, rather with respect to those which fall within it than to those which extend without it; and also rather for those which, in regard to the shortness of their extent, would not pass out of the said space than for those which would. And again, rather for lines of some considerable length than for any thing very short, for the inequality of lengths is less perceptible in great extents than the difference of configuration. For example, if you give 3000 stadia for the breadth at the Taurus, as well as for the sea which extends to the Pillars of Hercules, you will form a parallelogram entirely enclosing both the mountains of the Taurus and the sea; if you divide it in its length into several other parallelograms, and draw first the diagonal of the great parallelogram, and next that of each smaller parallelogram, surely the diagonal of the great parallelogram will be regarded as a line more nearly parallel and equal to the side forming the length of that figure than the diagonal of any of the smaller parallelograms: and the more your lesser parallelograms should be multiplied, the more will this become evident. Certainly, it is in great figures that the obliquity of the diagonal and its difference from the side forming the length are the less perceptible, so that you would have but little scruple in taking the diagonal as the length of the figure. But if you draw the diagonal more inclined, so that it falls beyond both sides, or at least beyond one of the sides, then will this no longer be the case; and this is the sense in which we have observed, that when you attempted to draw even in a very general way the extents of the figures, you ought to adopt some rule. But Eratosthenes takes a line from the Caspian Gates along the mountains, running as it were in the same parallel as far as the Pillars, and then a second line, starting directly from the mountains to touch Thapsacus; and again a third line from Thapsacus to the frontiers of Egypt, occupying so great a breadth. If then in proceeding you give the length of the two last lines [taken together] as the measure of the length of the district, you will appear to measure the length of one of your parallelograms by its diagonal. And if, farther, this diagonal should consist of a broken line, as that would be which stretches from the Caspian Gates to the embouchure of the Nile, passing by Thapsacus, your error will appear much greater. This is the sum of what may be alleged against Eratosthenes.
38. In another respect also we have to complain of Hipparchus, because, as he had given a category of the statements of Eratosthenes, he ought to have corrected his mistakes, in the same way that we have done; but whenever he has any thing particular to remark, he tells us to follow the ancient charts, which, to say the least, need correction infinitely more than the map of Eratosthenes.
The argument which follows is equally objectionable, being founded on the consequences of a proposition which, as we have shown, is inadmissible, namely, that Babylon was not more than 1000 stadia east of Thapsacus; when it was quite clear, from Eratosthenes’ own words, that Babylon was above 2400 stadia east of that place; since from Thapsacus to the passage of the Euphrates where it was crossed by Alexander, the shortest route is 2400 stadia, and the Tigris and Euphrates, having encompassed Mesopotamia, flow towards the east, and afterwards take a southerly direction and approach nearer to each other and to Babylon at the same time: nothing appears absurd in this statement of Eratosthenes.
39. The next objection of Hipparchus is likewise false. He attempts to prove that Eratosthenes, in his statement that the route from Thapsacus to the Caspian Gates is 10,000 stadia, gives this as the distance taken in a straight line; such not being the case, as in that instance the distance would be much shorter. His mode of reasoning is after this fashion. He says, “According to Eratosthenes, the mouth of the Nile at Canopus,600 and the Cyaneæ,601 are under the same meridian, which is distant from that of Thapsacus 6300 stadia. Now from the Cyaneæ to Mount Caspius, which is situated close to the defile602 leading from Colchis to the Caspian Sea, there are 6600 stadia,603 so that, with the exception of about 300 stadia, the distance from the meridian of the Cyaneæ to that of Thapsacus, or to that of Mount Caspius, is the same: and both Thapsacus and Mount Caspius are, so to speak, under the same meridian.604 It follows from this that the Caspian Gates are about equi-distant between Thapsacus and Mount Caspius, but that the distance between them and Thapsacus is much less than the 10,000 stadia mentioned by Eratosthenes. Consequently, as the distance in a right line is much less than 10,000 stadia, this route, which he considered to be in a straight course from the Caspian Gates to Thapsacus, must have been a circumbendibus.”
To this we reply, that Eratosthenes, as is usual in Geography, speaks of right lines, meridians, and parallels to the equator, with considerable latitude, whereas Hipparchus criticizes him with geometrical nicety, as if every line had been measured with rule and compass. Hipparchus at the same time himself frequently deciding as to right lines and parallels, not by actual measurement, but mere conjecture. Such is the first error of this writer. A second is, that he never lays down the distances as Eratosthenes has given them, nor yet reasons on the data furnished by that writer, but from mere assumptions of his own coinage. Thus, where Eratosthenes states that the distance from the mouth of the [Thracian Bosphorus] to the Phasis is 8000 stadia, from thence to Dioscurias 600 stadia,605 and from Dioscurias to Caspius five days’ journey, (which Hipparchus estimates at 1000 stadia,) the sum of these, as stated by Eratosthenes, would amount to 9600 stadia. This Hipparchus abridges in the following manner. From the Cyaneæ to the Phasis are 5600 stadia, and from the Phasis to the Caspius 1000 more.606 Therefore it is no statement of Eratosthenes that the Caspius and Thapsacus are under the same meridian, but of Hipparchus himself. However, supposing Eratosthenes says so, does it follow that the distance from the Caspius to the Caspian Gates, and that from Thapsacus to the same point, are equal.607
40. In the second book of his Commentaries, Hipparchus, having again mooted the question concerning the mountains of the Taurus, of which we have spoken sufficiently, proceeds with the northern parts of the habitable earth. He then notices the statement of Eratosthenes concerning the countries situated west of the Euxine,608 namely, that the three [principal] headlands [of this continent], the first the Peloponnesian, the second the Italian,