Kind of boring, but I thought I'd throw this out. I've been seeing comments on the impact of fireball on combat in other threads, and decided to post some of my thoughts on why it ain't all that (it can be effective, yes, but a competent army will by and large avoid the impact fireballs can have).
Fireball Tactics
To the uninitiated, high-power area effect spells seem like they should dominate any battle field. Fireball, easily the weakest of any arcanist's grimoire, fills an area large enough to house an entire company of soldiers with flames hot enough to burn a person to death in under a second. A five-company force (roughly 500 soldiers) could be decimated by a single arcanist in less than a minute.
For the student of military history, however, such spells are only occasionally useful against those unprepared or insufficiently intelligent to devise countermeasures.
Shields High: The Theralis shield wall is roughly four soldiers deep (shields, spears, longspears, support). In the area covered by a fireball, there will be a rough maximum of 60 soldiers, and a more typical number of 50. Of those, 15 are the shield wall, and another 10-15 carry additional shields. Once Theralis got over the shock of seeing orc shamans throw area destruction spells, they began step locking their shields and preparing for it. When the spells come, everyone leans into the shield wall (which leans back), while the Theralese in the back raise their shields behind. The result is something like a brief turtle moment, giving nearly 75% cover (100% for those closest to the shields) against the spells... and a tendency for the orcs on the other side of the shield wall to eat most of the spell themselves.
Scattered: Well behind the shield walls, the Theralese military remains widely spread - at most, an area spell will catch 20 people in the same area, a rather severe waste of the energy required to cast the spell. The orcs do much the same, and their chaotic nature belies their capacity for maintaining spreads instead of knots.
Counterstrikes: As demonstrated recently, the most effective countermeasure is a counterstrike. Spells can be traced, and once traced, return fire will either destroy the caster or persuade her not to do it again.
As an example, in the last Battle of Theralis Ridge, Greppa was put on fireball duty... not to throw them, but to target anyone among the orcs who did. That he did his job well is evident in the orcs' frustrated attempt to take him out so they could get on with the attack - the astute observer will note that when they failed to take him out... they also decided not to attack.