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 and the Ganges:  they heard that the seat of empire was, where it always has been, on the Ganges or Indus:  they acquired intelligence of all the grand and leading features of Indian manners, policy, and religion [and he might have added, accurate information respecting the geography of the western parts of that country]:  they discovered all this by penetrating through countries, where, possibly, no Greek had previously set his foot; and they explored the passage by sea which first opened the commercial intercourse with India to the Greeks and Romans, through the medium of Egypt and the Red Sea, and finally to the Europeans, by the Cape of