There has been much controversy over time about Alexander the Great's ability as a leader. There are five surviving sourced for knowledge of Alexander, the most reliable two written by Arrian (though his admiration for Alexander sometimes caused bias in his writing) and Plutarch. As stated by CB Welles, "there have been many Alexanders. No account of him is all together wrong".
Bibliography
1) Bradley, P (1988), Ancient Greece Using Evidence, Cambridge University Press: Cambridge.
2) Stevens, V, Merchant, W, Hampson, M, Bradshaw, G, (2003), HSC Ancient History Macquarie Revision Guide, Macmillan Education Australia Pty Ltd.
3) Roberts, P, (2003), Excel HSC Ancient History Book 1, Pascal Press
4) http://faq.macedonia.org/history/alexander.the.great.html
5) http://members.aol.com/tomstp9/alex.html
6) http://www.e-classics.com/ALEXANDER.htm
7) http://www.fsmitha.com/h1/ch11.htm
8) http://www.royalty.nu/Europe/Balkan/Alexander.html
There is no question among historians that Alexander was a military genius:
"No soldier in history is more undisputedly great' than Alexander"
- Burn
There were two main aspects of his military brilliance, the first being his tactical insight and strategic planning. He was able to modify and adapt his tactics to suit each opponent and was not afraid to vary the disposition of his troops. At Granicus, he focused on cavalry, he used a larger army at Gaugamela to overcome the danger of being encircled, and at Hydaspes he substituted his cavalry for infantry to enable them to face the elephants. He made the phalanx formation mobile and was flexible in his approach, often taking the enemy by surprise and forcing them to change their plans such as at Gaugamela where he forced the Persians into rough, rocky terrain. Alexander also ensured that their communication lines were carefully guarded, so that any reinforcements were able to reach the main