Eratosthenes, however, measures the length of the
habitable earth by a line which he considers straight, drawn
from the Pillars of Hercules, in the direction of the Caspian
Gates and the Caucasus. The length of the third section,
by a line drawn from the Caspian Gates to Thapsacus,
and of the fourth, by one running from Thapsacus through
Heroopolis to the country surrounded by the Nile: this
must necessarily be deflected to Canopus and Alexandria,
for there is the last mouth of the Nile, which goes by the
name of the CanopicCanopus, near to Aboukir. or Heracleotic mouth. Whether
therefore these two lengths be considered to form one
straight line, or to make an angle with Thapsacus, certain it is that neither of them is parallel to the length of the
habitable earth; this is evident from what Eratosthenes has
himself said concerning them. According to him the length
of the habitable earth is described by a right line running
through the Taurus to the Pillars of Hercules, in the direction of the Caucasus, Rhodes, and Athens. From Rhodes to
Alexandria, following the meridian of the two cities, he says
there cannot be much less than 4000 stadia,It was a mistake common to Eratosthenes, Hipparchus, and Strabo,
to fancy that Rhodes and Alexandria were under the same meridian. The
Longitude of the two cities differs by 2° 22′ 45″. consequently there
must be the same difference between the latitudes of Rhodes
and Alexandria. Now the latitude of Heroopolis is about the
same as Alexandria, or rather more south. So that a line,
whether straight or broken, which intersects the parallel of
Heroopolis, Rhodes, or the Gates of the Caspian, cannot be
parallel to either of these. These lengths therefore are
not properly indicated, nor are the northern sections any
better.