Long ago a awesome battle was fought over the control of the three bridges and the valley behind it. Outnumbered the King lead his men into battle against the rebels who dare betray him. The battle lasted into the night and the fighting was long and hard, but sadly in the end the castle was defeated and burned to the ground.
Many years have past since, so the king has order you to rebuild the fortification to its former glory.
-Rebuild the fortifications around the three main bridges protecting the valley