The indestructibility of the Poneglyphs had a direct connection to the Iron Giant.
Oda Reveals One Piece's BIGGEST SECRET! HAKI is not what we thought it was! (One Piece 1122)
The short summary spoilers of One Piece chapter 1122 have finally hit the internet after a little hiatus, and they have confirmed a big theory about the poneglyphs and the black blades. However, the confirmation of the theory comes with some modifications, as it has also added Emeth or Iron Giant in the same bracket.
For the longest time, One Piece fans wondered about the indestructibility of the poneglyphs and how they could stand the test of time. It is then that an assumption was made that the poneglyphs were imbued or stored with Haki just like the black blades, but there was no evidence to support this theory.
Chapter 1122 might just confirm that storing or sealing Haki in components is a real thing in One Piece, and the first example of this was Emeth, the Iron Giant. Thus, not only would it prove the theory of poneglyphs and black blades working on the same principle, but it would also confirm that Haki is the highest ability in One Piece.
