Before I get to the meat of this topic, a quick little time line summary:
26 years ago, Gol D. Roger learns of his incurable disease and embarks on his voyage through the Grand Line with his crew.
23 Years Ago, Gol D. Roger and crew, after passing Sky Island at least (and having Roger deposit his message in the ancient language on the side of the belfry), reach Raftel and deposit "one piece" and learn of the "true history" of the world. Gol D. Roger also disbands his crew at this time and submits to the World Government.
22 years ago, Gol D. Roger is executed in Loguetown
20 years ago, Professor Clover and the scholars of Ohara are accused of crimes against the World Government, and a buster call used on Ohara, effectively destroying it.
Alright, well recently, in chapter 507 page 6 last panel, Gol D. Roger's first mate and vice captain, Silvers Raleigh, says that Roger was unable to decipher the Ancient Language.
However, on the previous page, 5 second panel, Raleigh confirms that he and the crew know the "true history." Since the Poneglyphs are all engraved in the Ancient Language, and since Roger was unable to decipher (only write), this leads to the first assumption: that Roger and Raleigh had a nakama (no translation here the word is meant to be nakama and translating to friend doesn't do it the justice it deserves in this manga) that could read the ancient language.
Now comes the tricky part, building upon that assumption. Who was this mysterious individual who could read the ancient language?
I propose that this mysterious individual was none other than our (and Robin's) beloved Professor Clover. I make this assumption based on what Raleigh says on page 7 in the first panel:
"We could never hope to match the intellect of a genius like Clover, or or the scholars of Ohara."
Raleigh speaks of Clover as though he is a buddy, going so far as to separate him from the scholars in Ohara. Why would Raleigh specifically mention Clover if he did not know him at one point? How did the pirates really come to learn the true history? They had to have someone on the ship who could read the ancient language, and I am going to assume to that Raleigh's familiarity with Clover is due to the fact that Clover was in fact a nakama on that ship.
There is also Raleigh's cryptic message in the last panel of page 5 where he says "we….and the people of Ohara might have been too hasty," almost directly implying that the knowledge was shared between the two. If this is true, there had to be a connection. Why not the strong Clover, who was able to stand after being shot face to face?
Raleigh mentioned how Roger secretly disbanded his crew, and due to the doctor on the twin capes being uncaught, we can assume that some of his crew wasn't directly known by the World Government. Raleigh also mentioned how the disbanded crew didn't really keep in touch.
I believe that 23 years ago, Roger disbanded his crew which included Clovis, and Clovis went to Ohara where he recruited people to fully understand the true history for the next 3 years.
One chink in this theory is the idea that if Clovis did read the Rio Poneglyph, he wouldn't need to know the true history. I counter first by asking what exactly the Rio Poneglyph is. Robin has hinted that it might merely be the connection of all the Poneglyphs, but if this true, then how could be "located" at Raftel if the Poneglyphs are scattered throughout the world?
However, some would counter this by saying the last piece is at Raftel, which is certainly a fair assumption. Let us assume this is true for the moment. If this is the case, then that means it must hold the most important piece of information.
Note when Clovis was explaining what he referred to as a theory to the World Government, he stated that he knew the name of the ancient kingdom. Is it not fair to assume that the last piece would have the most important piece of information, the name of this kingdom, the name that could do such harm to the World Government?
I hypothesize that Clovis did in fact read the Poneglyph on Sky Island, and he did in fact read the "last piece," the Rio Poneglyph. However, what he read was not the complete history, but simply what he learned from the Poneglyphs that he read and the Rio Poneglyph. He hypothesized the rest and returned to Ohara to discover the rest of the Poneglyphs.
Thoughts?
I'd really like to hammer out what exactly the Rio Poneglyph is (as in if it is just what Robin told us and all the Poneglyph together or if it is something special on Raftel), and discuss the significance of the name of the Ancient Kingdom if I am correct and its name was the information written on whatever was there at the end on Raftel.
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Well, this is my first post in these forums, so I'll just say hi to Arlong Park! ^_^
Also, I'll be the first to admit that my knowledge of One Piece is limited to first time reading of the manga and viewing of the anime, and there are certainly factors that I might have misinterpreted or forgotten, so if there is a clear answer to this, I apologize in advance. I also apologize if this was better suited for the "theories that don't deserve their own thread" topic; I just think that the Ancient Kingdom is vital and will soon become a huge part of One Piece, so any connection / relation to it should be discussed by any fan of One Piece.
Finally, I posted this in another site, but that specializes in another Manga, so I figured I might as well post my thoughts in a One Piece specific place as well. If you see this thread somewhere else...don't worry! It was me!