Instructions
Proceed through the game until you're battling at Bethla Garrison. You start on low ground beneath the floodgates. Your goal is to get to the top and flip both switches using Ramza.
Cut a swath up to the gate. You have two routes, either on the left or the right side. Parties that specialize in melee attacks can most readily take down the mages and priest on the left side, while balanced parties can wear down the soldiers to the right.
Kill the remaining defenders on top. Because you're fighting atop a narrow platform, send your strongest melee fighter to lead the attack, while backing him up with ranged and magical assaults.
Move Ramsa onto the closest switch. It's the wooden platform on the edge of the dam. End his turn there to flip it.
Flip the other switch in the same manner as above and the floodgate will open.