[Master Shake]

Massed missile troops are standard fair for multiplayer games. They are exceedlingly effective against the AI, and very good against human opponents as well. So if you are up against a human, they will likely also have massed missile armies.

So then the question is how to effectively win in a such a massed archer fight. Wind Guide and Flame Arrows are extremely effective spells to increase the effectiveness of your archers/crossbowmen. As mentioned, Storm and Arrow Fend are common spell counters. There are also Deth Magic and Water Magic spells (I think on the water - it's not my favorite line) that limit range. Then, there are the really cool spells like Mistform and Massflight (Air spells) that would also wipe out a Crossbow amry. Massflight allows all troops to fly - imagine 50 Heavy infantry immediately flying adjacent to your 50 Crossbowmen.

In addition to these spells, there are battle orders you can give that help. One that is sometimes overlooked is Fire Enemy Archers. A large group of indy archers or longbowmen set to Fire Archers could devestate your massed Crossbowmen. Also, a group of flanking heavy cavlary can also wipe out massed missile troops if there are no heavy infantry or spells to stop them.