Susa, the three routes through the different provinces, and the navigation
along the coast, might be said to complete the survey of the empire."

The two divisions of his army were accompanied on their return to Susa by
Beton and Diognetus, who seem to have united the character and duties of
soldiers and men of science; or, perhaps, were like the quarter-masters-
general of our armies. It appears from Strabo and Pliny, in whose time the
surveys drawn by Beton and Diognetus were extant, that they reduced the
provinces through which they passed, as well as the marches of the army, to
actual measurement; and thus, the distances being accurately set down, and
journals faithfully kept, the principles of geographical science, next in
importance and utility to astronomical observations, were established. The
journals of Beton and Diognetus, the voyage of Nearchus, and the works of
Ptolemy, afterwards king of Egypt, and Aristobulus, who accompanied
Alexander in his expedition and wrote his life, all prove that the
authority or the example of the sovereign influenced the pursuits of his
officers and attendants; and it is highly to the credit of their diligence
and accuracy, that every increase of geographical knowledge tends to
confirm what they relate respecting the general appearance and features of
the countries they traversed, as well as the position of cities, rivers,
and mountains.

Alexander appears to have projected or anticipated an intercourse between
India and the western provinces of his dominions in Egypt, not only by land
but by sea: for this latter purpose he founded two cities on the Hydaspes
and one on the Axesimes, both navigable rivers, which fall into the Indus.
And this also, most probably, was one reason for his careful survey of the
navigation of the Indus itself. When he returned to Susa, he surveyed the
course of the Tigris and Euphrates. The navigation near the mouths of those
rivers was obstructed by cataracts, occasioned by walls built across them
by the ancient monarchs of Persia, in order to prevent their subjects from
defiling themselves by sailing on the ocean[4]: these obstructions he gave
directions to be removed. Had he lived, therefore, the commodites of India
would have been conveyed from the Persian Gulf into the interior provinces
of his Asiatic dominions, and to Alexandria by the Arabian Gulf.

To conclude in the words of Dr. Vincent: "The Macedonians obtained a
knowledge both of the Indus