I asked a lot of questions before the RP began Dinh.  The pass is actually wide enough for our small army of 1200 soldiers to fit comfortably in it, and allows up ample room to maneuver such units as cavalry.  That's not an issue.  To pull off something like you see in the Battle of Thermopylae isn't viable either, as our forces would be stretched way to thin in order cover the width of the pass.

One of the other player's did scale the rocks and spied inside of the enemy's base successfully, but I'm afraid the GM is going to use the landslides against us (yes, he said landslides are possible).

Also, this pass is significant in that it is the only sure way to pass through these mountains which separate the east and the west (the east has been conquered and that empire is now marching on the west, and the players are military leaders from the west who band together to delay the invasion while our actual armies can mobilize to meet the bulk of the empire's forces as a whole).  Because of this, I'm not really afraid of being attacked from the rear.  Imagine a moderately-sized battlefield, but when you left said battlefield you can only march east or west - not north or south.

It should be noted that I arrived to the second battle late because:
1.  My second-in-command killed my commander in combat, and then assumed control of my forces, and
2.  Some of my soldiers were sent into the wilderness and successfully returned with pigs (farmland pigs).

I had thought of a phantom strategy to goad the GM into deploying a mass of archers; I would send out light skirmishers to disrupt the enemy... but the real strategy is to not move the skirmishers and instead send out a large group of warriors who can form a shield wall, rendering the arrows useless.  As the enemy archers retreat, our cavalry will go around the shield wall and flank whatever infantry they may have.