There has been something about the Ancient Weapons that has been bugging me, if they were supposedly made by the Ancient Kingdom, and that kingdom was wiped out by the 20 kingdom alliance, how did the 20 kingdoms wipe them out when the Ancient Kingdom had such power at their disposal?
Here's my theory, the Ancient Kingdom built the weapons, feeling threatened, the twenty kingdoms stole the designs, built them for themselves, and used them to take out the Ancient Kingdom. Once the Ancient Kingdom was gone, they destroyed their weapons to maintain power, but kept the blueprints. They didn't learn about the poneglyphs until later.
That's my theory, although it's not the most concrete. Prove me wrong or tell me otherwise.