22. Again, Hipparchus, ever anxious to defend the [accuracy of the] ancient charts, instead of fairly stating the words of Eratosthenes concerning his third section of the habitable earth, wilfully makes him the author of an assertion easy of disproof. For Eratosthenes, following the opinion we before mentioned, that a line drawn from the Pillars of Hercules across the Mediterranean, and the length of the Taurus, would run due west and east,549 divides, by means of this line, the habitable earth into two portions, which he calls the northern and southern divisions; each of these he again essays to subdivide into as many smaller partitions as practicable, which he denominates sections.550 He makes India the first section of the southern part, and Ariana551 the second; these two countries possessing a good outline, he has been able not only to give us an accurate statement of their length and breadth, but an almost geometrically exact description of their figure. He tells us that the form of India is rhomboidal, being washed on two of its sides by the southern and eastern oceans [respectively], which do not deeply indent its shores. The two remaining sides are contained by its mountains and the river [Indus], so that it presents a kind of rectilinear figure.552 As to Ariana, he considered three of its sides well fitted to form a parallelogram; but of the western side he could give no regular definition, as it was inhabited by various nations; nevertheless he attempts an idea of it by a line drawn from the Caspian Gates553 to the limits of Carmania, which border on the Persian Gulf. This side he calls western, and that next the Indus eastern, but he does not tell us they are parallel to each other; neither does he say this of the other sides, one bounded by the mountains, and the other by the sea; he simply calls them north and south.
23. Having in this manner but imperfectly traced the outlines of his second section, the third section, for various reasons, is still less exact. The first cause has been already explained, viz. that the line from the Caspian Gates to Carmania is not clearly defined, as the side of the section is common both to the third and second sections. Secondly, on account of the Persian Gulf interrupting the continuity of the southern side, as he himself tells us, he has been obliged to take the measured road running through Susa and Persepolis to the boundaries of Carmania and Persia, and suppose it straight.554 This road, which he calls the southern side, is a little more than 9000 stadia. He does not, however, tell us, that it runs parallel to the northern side. It is also clear that the Euphrates, which he makes the western boundary, is any thing but a straight line. On leaving the mountains it flows south, but soon shifts its course to the east; it then again pursues a southerly direction till it reaches the sea. In fact, Eratosthenes himself acknowledges the indirect course of this river, when he compares the shape of Mesopotamia, which is formed by the junction of the Tigris and Euphrates, to the cushion on a rower’s bench. The western side bounded by the Euphrates is not entirely measured; for he tells us that he does not know the extent of the portion between Armenia and the northern mountains,555 as it has not been measured. By reason of these hinderances he states that he has been only able to give a very superficial view of the third section, and that his estimate of the distances is borrowed from various Itineraries, some of them, according to his own description, anonymous. Hipparchus therefore must be considered guilty of unfairness, for criticising with geometrical precision a work of this general nature. We ought rather to be grateful to a person who gives us any description at all of the character of such [unknown] places. But when he urges his geometrical objections not against any real statement of Eratosthenes, but merely against imaginary hypotheses of his own creation, he shows too plainly the contradictory bent of his mind.
24. It is in this general kind of description of the third section that Eratosthenes supposes 10,000 stadia from the Caspian Gates to the Euphrates. This he again divides according to former admeasurements which he found preserved. Starting from the point where the Euphrates passes near to Thapsacus, he computes from thence to the place where Alexander crossed the Tigris 2400 stadia. The route thence through Gaugamela,556 the Lycus,557 Arbela,558 and Ecbatana,559 whither Darius fled from Gaugamela to the Caspian Gates, makes up the 10,000 stadia, which is only 300 stadia too much. Such is the measure of the northern side given by Eratosthenes, which he could not have supposed to be parallel to the mountains, nor yet to the line drawn from the Pillars of Hercules through Athens and Rhodes. For Thapsacus is far removed from the mountains, and the route from Thapsacus to the Caspian Gates only falls in with the mountains at that point.560 Such is the boundary on the northern side.
25. Thus, says Eratosthenes, we have given you a description of the northern side; as for the southern, we cannot take its measure along the sea, on account of the Persian Gulf, which intercepts [its continuity], but from Babylon through Susa and Persepolis to the confines of Persia and Carmania there are 9200 stadia. This he calls the southern side, but he does not say it is parallel to the northern. The difference of length between the northern and southern sides is caused, he tells us, by the Euphrates, which after running south some distance shifts its course almost due east.
26. Of the two remaining sides, he describes the western first, but whether we are to regard it as one single straight line, or two, seems to be undecided. He says,—From Thapsacus to Babylon, following the course of the Euphrates, there are 4800 stadia; from thence to the mouth of the Euphrates561 and the city of Teredon, 3000562 more; from Thapsacus northward to the Gates of Armenia, having been measured, is stated to be 1100 stadia, but the distance through Gordyæa and Armenia, not having yet been measured, is not given. The eastern side, which stretches lengthwise through Persia from the Red Sea towards Media and the north, does not appear to be less than 8000 stadia, and measured from certain headlands above 9000, the rest of the distance through Parætacena and Media to the Caspian Gates being 3000 stadia. The rivers Tigris and Euphrates flowing from Armenia towards the south, after having passed the Gordyæan mountains, and having formed a great circle which embraces the vast country of Mesopotamia, turn towards the rising of the sun in winter and the south, particularly the Euphrates, which, continually approaching nearer and nearer to the Tigris, passes by the rampart of Semiramis,563 and at about 200 stadia from the village of Opis,564 thence it flows through Babylon, and so discharges itself into the Persian Gulf. Thus the figure of Mesopotamia and Babylon resembles the cushion of a rower’s bench.—Such are the words of Eratosthenes.
27. In the Third Section it is true he does make some mistakes, which we shall take into consideration; but they are nothing like the amount which Hipparchus attributes to him. However, we will examine his objections. [In the first place,] he would have the ancient charts left just as they are, and by no means India brought more to the south, as Eratosthenes thinks proper. Indeed, he asserts that the very arguments adduced by that writer only confirm him the more in his opinion. He says, “According to Eratosthenes, the northern side of the third section is bounded by a line of 10,000 stadia drawn from the Caspian Gates to the Euphrates, the southern side from Babylon to the confines of Carmania is a little more than 9000 stadia. On the western side, following the course of the Euphrates, from Thapsacus to Babylon there are 4800 stadia, and thence to the outlets of the river 3000 stadia more. Northward from Thapsacus [to the Gates of Armenia] is reckoned 1100 stadia; the rest has not been measured. Now since Eratosthenes says that the northern side of this Third Section is about 10,000 stadia, and that the right line parallel thereto drawn from Babylon to the eastern side is computed at just above 9000 stadia, it follows that Babylon is not much more than 1000 stadia east of the passage of [the Euphrates] near Thapsacus.”
28. We answer, that if the Caspian Gates and the boundary line of Carmania and Persia were exactly under the same meridian, and if right lines drawn in the direction of Thapsacus and Babylon would intersect such meridian at right angles, the inference would be just.565 For then the line [from the common frontier of Carmania and Persia] to Babylon, if produced to the meridian of Thapsacus, would appear to the eye equal, or nearly equal, to that from the Caspian Gates to Thapsacus. Consequently, Babylon would only be east of Thapsacus in the same proportion as the line drawn from the Caspian Gates to Thapsacus exceeds the