Read the Theory bellow at your own expenses, as I will refer to events in the manga that have not yet occurred in the Anime, and are rather fresh.
What is One Piece? Undoubtedly there is something bigger at the end of the Grand Line than simply a huge treasure left by the Pirate King, Gol D. Roger. The fact that all Log Poses eventually end up pointing to it, and the fact that the trail of Phoneglyphs end in Raftel, the end of the Grand Line, would make it a matter of great importance. But despite all the technology, both Pirate and Marine alike, only Gol D. Roger was able to reach it.
In fact, in one of his last conversations with Whitebeard, Roger mentioned that there is a special way to reach it, meaning not even someone as powerful as Whitebeard would be able to do it.
Now, as Reyleigh said, Roger had the ability to hear the "Voice of All Things". We knew it translated in not being able to Read the phonglyph, but nonetheless understand their purpose, as if hear their messages. With the risk of going off topic, that alone could mean that there is something special about their origin, not just made out of indestructible materials). In the recent chapter, we discovered that Roger could also hear Sea Kings (And Luffy can too, so he is inheriting the same power).
Now, the Sea Kings are responsible to drag Noah, which is directly connected with Joy Boy, whose letter is written in the Phoneglyph at Fishman Island. So there is some sort of connection between Sea Kings and the Void Century.
Now, following the same pattern as one of my previous theories, what was the ancient civilization trying to protect? And this is what i came up with:
Either as a bless from a God or a bless from a Demon, a tree grew in an island, in my opinion, Raftel. This three would grow beautiful and strange fruits, but would taste extremely bad. Soon the ones who ate the fruits would discover that they had acquired strange and magnificent powers, but would be repelled by the Sea. Soon the whole kingdom revolved around it. Mad with power, some people of the kingdom tried to take over the tree, and keep the power all to themselves, but others knew the power was evil, and had to be forbidden.
There was a great civil war which ended up in the victory of the protectors of the tree. At that point, the Sea Kings were created, and Raftel became impossible to reach. The tree would remain there, it's long branches reaching over the sea, dropping the mature fruits into the ocean currents, bringing them to all corners of the world. Instead of having everyone eat the fruits and get drunk in power, now only a few ones would be stroke by the curse or bless. In this part, I can have a few branched theories. One, the Sea Kings already existed, nesting in the Calm Belts, but a few especial ones were hand picked, Sea Kings with intelligence and power far superior to the others, ruled by a Queen. They settled down in Raftel and protected the Tree. Also, either the currents or the Sea Kings would have the job to bring the fruits to the corners of the World.
The came the 20 Kings, maybe descendants of the people who tried to keep the tree to themselves to acquire greater power. And they tried to reach Raftel. Then the huge battle took place, with the ancient weapons, and took over the whole world. In the end, the 20 Kings won over the ancient Kingdom, and it's people were killed or banished, and the World Government too place. But before that were to happen, they used the weapons to drastically change the world, creating the wacky Grandline and making Raftel impenetrable, while keeping the Sea Kings and the Phoneglyphs to guide the way of the chosen one, who would bring peace to the world.
Reading back on the theory, it is not very good. So the only things that I would like to keep from it is that the tree of all Devil Fruits is at the end of the Grand Line, and the reason why the rare fruits are found all over the world is because they travel the Sea Currents, or are brought in the mouth of the Sea Kings.
What is One Piece? Undoubtedly there is something bigger at the end of the Grand Line than simply a huge treasure left by the Pirate King, Gol D. Roger. The fact that all Log Poses eventually end up pointing to it, and the fact that the trail of Phoneglyphs end in Raftel, the end of the Grand Line, would make it a matter of great importance. But despite all the technology, both Pirate and Marine alike, only Gol D. Roger was able to reach it.
In fact, in one of his last conversations with Whitebeard, Roger mentioned that there is a special way to reach it, meaning not even someone as powerful as Whitebeard would be able to do it.
Now, as Reyleigh said, Roger had the ability to hear the "Voice of All Things". We knew it translated in not being able to Read the phonglyph, but nonetheless understand their purpose, as if hear their messages. With the risk of going off topic, that alone could mean that there is something special about their origin, not just made out of indestructible materials). In the recent chapter, we discovered that Roger could also hear Sea Kings (And Luffy can too, so he is inheriting the same power).
Now, the Sea Kings are responsible to drag Noah, which is directly connected with Joy Boy, whose letter is written in the Phoneglyph at Fishman Island. So there is some sort of connection between Sea Kings and the Void Century.
Now, following the same pattern as one of my previous theories, what was the ancient civilization trying to protect? And this is what i came up with:
Either as a bless from a God or a bless from a Demon, a tree grew in an island, in my opinion, Raftel. This three would grow beautiful and strange fruits, but would taste extremely bad. Soon the ones who ate the fruits would discover that they had acquired strange and magnificent powers, but would be repelled by the Sea. Soon the whole kingdom revolved around it. Mad with power, some people of the kingdom tried to take over the tree, and keep the power all to themselves, but others knew the power was evil, and had to be forbidden.
There was a great civil war which ended up in the victory of the protectors of the tree. At that point, the Sea Kings were created, and Raftel became impossible to reach. The tree would remain there, it's long branches reaching over the sea, dropping the mature fruits into the ocean currents, bringing them to all corners of the world. Instead of having everyone eat the fruits and get drunk in power, now only a few ones would be stroke by the curse or bless. In this part, I can have a few branched theories. One, the Sea Kings already existed, nesting in the Calm Belts, but a few especial ones were hand picked, Sea Kings with intelligence and power far superior to the others, ruled by a Queen. They settled down in Raftel and protected the Tree. Also, either the currents or the Sea Kings would have the job to bring the fruits to the corners of the World.
The came the 20 Kings, maybe descendants of the people who tried to keep the tree to themselves to acquire greater power. And they tried to reach Raftel. Then the huge battle took place, with the ancient weapons, and took over the whole world. In the end, the 20 Kings won over the ancient Kingdom, and it's people were killed or banished, and the World Government too place. But before that were to happen, they used the weapons to drastically change the world, creating the wacky Grandline and making Raftel impenetrable, while keeping the Sea Kings and the Phoneglyphs to guide the way of the chosen one, who would bring peace to the world.
Reading back on the theory, it is not very good. So the only things that I would like to keep from it is that the tree of all Devil Fruits is at the end of the Grand Line, and the reason why the rare fruits are found all over the world is because they travel the Sea Currents, or are brought in the mouth of the Sea Kings.