Epaminondas for me. Reading the wiki article on him and what those familiar with the name you would think he started a revolution on Greek warfare by breaking convictions and showing the staunch conservative Spartans what true innovation looks like. However upon close inspection it appears Epaminondas did nothing new at Leuktra. Whatever innovations people credit to him are attested, even the "conservative" Spartans beat him to the punch.
One of his supposed innovations was leading from the left rather than the right thus making a tactical innovation here. The problem here is that this is simply false. Dr. Konijnendijk in his book
Classical Greek Tactics: A Cultural History
tallied up where Greek armies led from what our sources tell us. Surprisingly it turns out leading from the center and the left was more numerous than leading from the right. Ironically the first time we hear of a land army being led from the left came from the Spartans, beating Epaminondas by decades.
Another critical innovation is that Epaminondas led the way by amassing his hoplites in a deep formation of 50 ranks. But the kicker here is that he wasn't the first to do so. The forces under the Thirty Tyrants amassed their hoplites 50 or so ranks deep when facing off against the democratic rebels of Athens years earlier. To either of these accounts Xenophon offers no sense of awe or comment. In contrast Xenophon was quiet eager to tell the other Greeks of Spartan practices like their organization or their formation drill and he even stops his narrative to explain these alien custom to the other Greeks. Similarly we are told the Thebans formed up deep at Delium yet Thukydides doesn't present this as some innovation but when it came to describing how the Spartans managed to march in step to the sound of flutes during the second battle of mantinea he stop his narrative to describe in awe this Spartan practice.
What Epaminondas did do was make good use of know practices against the Spartans. The Spartans were not invincible and were probably not better fighters than the other Greeks. Battles like Leuktra and Tegyra showed that just standing up to the Spartans could throw their battle plan in disarray. The Spartans relied on psychological warfare in order to win battles, in our sources there's, iirc, three times the Spartans won major battles without having to fight because their enemies fled in sheer terror, at one point even crushing and trampling one another trying to flee the Spartans.
Aut viam inveniam aut faciam.
Will not change sig until the Tsar is put back in the Russian throne (July 08, 2010)
