Scattered among the islands of the Grand Line are mysterious stone blocks called "Poneglyphs."
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.
The poneglyph tells the location of Pluton. Nico Robin never wanted to give Crocodile the ancient weapon so she lied by telling the history of the land which is not found in the Poneglyph.  Robin was looking for the True History, not Pluton, so she lost her will to continue on. However, she was saved by Luffy.
Filler Arabasta Poneglyph
In the anime filler, Chopper, Luffy and Zoro get lost in the desert somewhere and fall in the hole where the poneglyph is half-buried. However, this poneglyph is not a canon one, as it is only in the anime.
Poneglyph of Shandora
The Poneglyph of Shandora is 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. Gol D. 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.
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.
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.