In the back and forth agenda fueled power scaling debates something caught my eye. Roger only went for the RPs after he had completed the Grand Line once already. I think in the Zou arc we learned that the compasses only lead to Lodestar and that is where the significance of RPs was revealed to Roger Pirates (I might be remembering wrong though). So this begs the question that if RPs were not important before Roger Pirates learned about it at Lodestar then how did BM come to know of it and had one in her keeping already?
Had there been other pirates who had finished the Grand Line before Roger Pirates and knew of the importance of RPs and BM learned from them?
Did BM learn about them from her time in Rocks Pirates?
Did Rocks know about them and he told others or BM secretly learn from him?
Some inaccuracies here.
Roger
didn't complete the Grand Line, multiple times, he did it once. Lodestare was the start of it.
Completing the Grand Line includes going to Laughtale, that's pretty much what it means to be Pirate King.
What Roger did if you re-read chapter 820 iirc is... he first went to Lodestar which is the Island the Log Pose points to.
Roger was the first to reach Lodestar Island, and Lodestar is where people learn about the significance of Poneglyphs (including Road Ponegylphs), Wano, the final Island (Laughtale) and the Ancient Language.
On reaching Lodestar, Roger discovered he had to completely plan anew his journey.
Rocks was defeated 40 years ago. He's the reason Big Mom was acquainted with the Road Poneglyphs most likely.
Kaido on the other hand was an apprentice at the time, and he only became interested in Poneglyphs about 4-5 years ago. Reason we know this is because Oden went to Laughtale, and Kaido killed him.
After killing Oden, 20 years later the scabbards re-appeared and then he started trying to capture and interrogate the secrets of Laughatale. Thing is he had the scabbards and Oden 20 years ago, so what happened after 20 years where he decided to no longer kill the scabbards, but acquire information?
Ace went to Wano, and Kaido wasn't around. All we know is Kaido went on a huge voyage which suggests this voyage is where he went to Lodestar Island, understood the significance of Poneglyphs and then the Scabbards re-appearing is when he realised he'd benefit more from interrogating than killing.
Even Whitebeard didn't know much about Poneglyphs or their significance, Roger told him about it when he fought him and then bargained to borrow Oden.
Rocks probably after some time realised that the Government's obsession with banning interest in Poneglyph pretty much gave away the fact that it was an important relic that needed to be deciphered. Pretty much, the streisand effect. In an attempt to take away attention from something, it actually gives it more attention.
We're also told Roger was the only one to ever reach Laughtale in the past 800 years, and was the first to reach Lodestar. This is why Roger is the greatest pirate. He did what no other Pirate could do. Chapter 0 also mentions this about Roger.
Big Mom and Shiki were 2 Pirates from Rocks who we know for sure knew the Poneglyphs were important. Big Mom herself didn't seem to really know why, but she understood it was sought out for a good reason. Shiki knew it was related to Ancient Weapons as well.
The entire thing is no one knows why the Poneglyphs are really important, but literally the entire story is about Peonglyphs. They contain the history of the world, secrets of the world, access to knowledge even Vegapunk needs to build the energy device that can power the world for free. It's the answer to knowledge that will grant one power to take over the world.
It's not just historical knowledge that reveals the WG's dark past... bare in mind the WG is only in power because they've lied to the world. Finding the One Piece uncovers that which is only doable via Road Poneglyphs.
As we get closer to the end of the story, the importance of the Poenglyphs become more and more obvious. Even in chapter 846, Tamago actually tells us what the One Piece is. Road Poneglyphs lead to the "Real" (Japanese pronounce this as RIO) Poneglyphs. The collection of Poneglyphs that come together to reveal the true history of the world from history all the way to scientific advancement - One Piece. That's what all my reading of the story has led me towards anyway.
