I read mountain pass, and then read maneuvers that would be executed in open field. You don't really [i]flank[/i] anything when you're held up in a pass. You can't move, and neither can the other guy. Passes and narrow valleys such as this are really good at funneling people in one direction. Maybe you could scale the rock on either side, but that's a vulnerability issue. So frankly: your cavalry would be useless.

The advantage of holding a pass is that a defensive force can hold back another army ten times its size. You just don't break rank while you do it.

That said, you could feign retreat and just crush the other force with rocks from the side once they advance to gain ground. This'd probably narrow the pass even further and make it more of a grinder.

The loosing scenario though would be if he managed to find an alternate route to get at the army's caravan in behind and box you in.