When you're studying Alexander's conquests do consider the physical barriers he had to over come and not just of distance.
Take a look at this map.
Alexander's armies and navies had to cross the Mediterranean and the Mountains of Asia Minor then move across the highlands of Persia and deserts to reach India.
Terrain this diverse also partly explains why his empire broke up into the lesser realms of the Diadochii. Ptolemy wisely claimed Egypt protected by deserts. The Seleucids tried to control Asia Minor and Mesopotomia and further east but lost the east to the Parthians.
One of the most successor Hellenistic era generals were not a Seleucid or Antigonid or Ptolemy. Our next post discusses Pyrrhus of Epirus.