Poneglyph

Scattered among the islands of the Grand Line are mysterious stone blocks called "Poneglyphs."

About
These blocks are inscribed with the script of an ancient language, and tell of a history long forgotten. This history includes the mention of (at least) two weapons of mass destruction: Pluton and Poseidon. There are two types of Poneglyphs: the ones which carries information to reach the other Poneglyphs, which tell the True History and the ones which carries the records of True History. It has been revealed that it is against the law of the One Piece World Government to decipher them. Regardless, to reach and decipher the Rio Poneglyph is the ultimate goal of Nico Robin. It has also been revealed that Gol D. Roger was able to read poneglyphs.

Alabasta Poneglyph
This was the Poneglyph that contained the location of the weapon Pluton and was located in the country of Alabasta in its royal tombs. The people of Alabasta have been guarding its Poneglyph for centuries. Robin revealed to King Cobra what it was, the King knew it held a weapon but had no idea that the Blank Century it came from existed.

Poneglyph of Shandora
Located in Skypiea, Robin discovered that each location of the Poneglyphs held not one but two Poneglyphs. The first Poneglyph has a message to finding the second Poneglyph, while the second Poneglyph held the message of the lost century. Skypiea's fake poneglyph was located in a set of ruins Robin found in Upper Yard. Skypiea's true Poneglyph was located on its sacred bell and it revealed to Robin another dark secret -this poneglyph spoke of how to locate yet another weapon, Poseidon. Gold Roger had also previously read this Poneglyph and left a message encouraging anyone who could read the Poneglyphs to continue searching for the lost history. The Shandians were left to guard the Poneglyph but over time as events in Skypiea played out they forgot about its existence.

Ohara Poneglyph
Located in Ohara, this poneglyph includes information about the Lost Century--among other things, it includes the name of the lost civilization, though it has yet to be said what the name is. The World Government considered the archaeologists studying it dangerous and used the Buster Call to destroy the island, Nico Robin being the sole survivor.

Rio Poneglyph
It is said that the Rio Poneglyph, which contains the true history of the One Piece world (including the "Blank Century" that is forbidden to be researched), may be found on the island of Raftel at the end of the Grand Line. Once found it will reveal the lost history from the Blank Century. According to Robin the Rio Poneglyph is the message carried by all the Poneglyphs along the Grand Line.