Re, Force sizes:
Actually it is mentioned in the annals that the force Ceasar commanded when he conquered Gaul was about 30'000 soldiers, and likely he commanded forces of similar size also elleswhere. This is a somewhat larger force then Alexanders army, and yes, the infrastructure and logistics of the Ancients put a very strict limit upon the biggest size of an army in conquest. When Scipio Africanus marched an army of 65'000 men and brought it over to Zama, south of Khartago, it was considered a remarkable take on the logistics (though it is not very likely that the full force were taken over the sea).
Re, Ceasar vs. Alexander
First of all, Caesar and Alexander are very different to compare for the reason that they were very different in their temperament, not just their thinking. I would see Ceasar as greater on one critical point, and that was that Ceasar was very concerned with Luck, and he knew as a general rule, that luck will come to you if you do like - like emperor Tiberius put it "A good shepherd cut the wool of the sheps, but he doesn't skin them". Clearly said: Alexander didn't know when it was time to stop, and therefore, he will count along the long row of other conquerors who in some way had to face a defeat of some kind. Alexanders defeat was when he entered India - a very vast way from home, not just with the Ancient measuring - and when not even this was enough for him, he wanted to go furthr to China, but then his soldiers refused to follow him, and he was forced to return home. ---- Caesar then, was one of the few conquerors of world history who never was defeted. The reason is exactly that Ceasar, who cried under Alexanders statue, and lived out all his emotions with a intense charisma as result, always has his common sence in judgements still there - he always could calmly calculate the risks of a conquest, and oppress his longing for eternal life. When Ceasar had conquered Gaul, he didn't continue into Germanic soil as such a conquest couldn't be estimated to occupy him for a certain time, he didn't attack Brittannia as the exact size of that continent wasn't known and that also would include a too large element of unsecurity and risk. On the other hand, he knew that he could conquer Gaul, adn he know he would win fame and a good strategic position from it, he didn't enter into Asia Minor as he knew the slumbering strength of the Persian Empire.... It seems that Ceasar always had the ability to choose the road to go that he had the best probabilities to be victorious, and above all the sharpness of mind to execute these conqests as smart as possible. Seemingly he only twice took on projects that were very risky. The first was when he crossed Rubicon and started the Civil War. He could at that point likely count with being victorious in the closest time, but the political and military consequences on a longer perspective must have been very hard to predict. The other case when he had practically won the Civil War, and he attacked Hispania to hunt down his antagonists last bastion. The leader of the republican forces in Hispania was a very intelligent man and a general with much experiance (the name escapes me and I don't have the sources at hand), and Caesar knew he could as likely win as loose. He still took on this campaign as he argued from Hispania a future threat against the Monarchy he tried to etablish could be raised, an he wished to complete his task on that point. Ceasar wrote in "De bello civil" that had he lost this battle he had sought his own death on the battlefield. ----An other difference between Ceasar and Alexander was also bound in temperament, and that was that Alexander acted mainly on impulse, as whole his nature and personality was impulsive, while Ceasar on the other hand planned everything he did like a perfectionist. Ceasar suffered from epilepsy, and at the day for one battle in Gaul, Ceasar was not able to lead his troops in the battle due to an epilepsyattack, still his plans which he had given to his officers were so exact that they could lead the army in his absence, and the fight went like a clockwork after his plans. ----
When one rates a military leader - of any time - two main things have to be considered: his ability as tactican and his ability as strategian. In short the difference is that strategy means taking overlaying desicions which causes the campaign as whole to turn out well, while a good tactican is good at simply concrete execute the plans. Like the strategian moves on the map, but the tactician moves on the battlefield. Hannibal is an example on a general who was a great tactican, but a poor strateg. He brilliantly understood the strengthness of his own armys discipline and the weakness of the enemy armys psyche, and therefore he could totaly destroy a Roman army with the highly original tactic in the battle of Cannae, but in his Italian campaign, he didn't realize that he could easily have won the war with attacking Rome at an early stage, instead he wasted his resources on a lot of messing around. His opponent OTOH, Fabius Maximus, knew exactly from the beginning that he could defeat Hannibal with fooling him to do exactly as he came to do. Fabius avoided to meet Hannibal in a big battle, and fooled him to waste his resources and time on attacking fortified cities, therefore Fabius was a good strateg (another insight F. had was that he wasn't as good tactican as Hannibal and would likely loose if their armies confronted openly). That Fabius maximus has to bear the nickname "Cunctator" (="the slow sausage"), is unfair.
Alexander made some very wise strategical desicions, like when he conquered the Palestine coast and Egypt before striking into Babylonia to prevent the Persians from attacking Greece in his back with fleets, but Alexander was also to much extent in a position where he could trust that his technically supreme infantry units - the phalanxes - would do the hard work. Many times he didn't need to plan extensively at all, it was just to drive over the enemy with this armoured beast, the phalanx, and the fight was won. Much also thanks to he had psychological overtake with countrymen who were very determined to win, meeting an yet bigger enemy force but consisting of soldiers from many coutries, many not very eager to fight for the Persians, and many who would even welcome a Greek victory for other reasons (mainly economical). Ceasar then had after anno 58 at least an enemy who was as determined as him to fight until last chance was outdone, adn he had to take many very good desicions strategically as well as tactically. Ceasar managed to do this, but so he was also an incredibly intelligent human being, and in my opinion more provenly a greater general then Alexander. The reasons I have explained above.
Mats Norrman
mats.norrman@home.se