When I say the most important battle I mean what battle changed the ancient world, be the results of that battle changed something be it political or military. I think that the most important battle of ancient history was the battle of the Milvian bridge. Just imagine how diffrent the world would be today if Constantine's army was crushed and Maxentius remained Emperor of Rome.
No Christianity in that scenario... Haven't thought about the real importance of that one... I think most people will answer the battle of Zama, Thermopylae or Philippi...
The last of the Byzantine-Sassanid wars. Heraclius' victory spelled the end of Zoroastrian Persia as a legitimate force, but severely weakened the empire in the process. Ultimately, the scale of the war meant that the Muslims were able to sweep across North Africa and Asia, setting the scene for the grand-scale conflict that would persist between Christianity and Islam for almost a millenia.
I would have to say the sacking of Rome. Before that point, spirits could not have been higher about saving the empire. Stilicho had accomplished everything he needed to accomplish to save the empire except defeat the unsurper Constantine (who surprisingly he had known personally like no other master general would know a random rogue soldier in Britain). Alaric had been appointed master general and seemed completely devoted to defeating Constantine and preserving the empire like the great Stilicho had almost been done accomplishing. Then Athaulf, Alarics brother, entered the empire and tried to suede him. At first Alaric was not persuaded, but the Galla Placidia began her smear campaign against the Germans in Italy, and basically had Alaric labeled an enemy to Rome, whihc forced Alaric to turn on ROme and sack it. If Alaric had not sacked Rome, and had instead been able to carry out his duty of being master general, I have no doubt in my mind that the Western Roman Empire would have been preserved for an extra 150-200 years.
I don't remember the name of the battle really, but that one between Epirus and Rome, where Pyrrhus won, but with so many losses that he stopped his campaign. If he won that battle with less losses the world as we know would be much different.
Imagine if Joshua got his ass handed to him in his campaign for the Promise Land? That would've been big. Christianity probably would've ended up like Judaism. Abused, prosecuted, and all that good stuff.
The battle of the ancient homosapiens. If the Ethiopian homosapiens didn't drive out the other band of homosapiens, the whole entire world would be different.
