What is the red line one piece?

The Red Line is a massive, mountain-like structure that runs horizontally across the world of One Piece, splitting the Grand Line in half. It is made up of incredibly hard, indestructible bedrock and stretches from the North Pole to the South Pole, separating the four seas that make up the world.

The Red Line is significant in the One Piece world because it is where the world's greatest powers, the World Government and the Marines, have their headquarters. It is also home to several powerful nations, such as Mariejois and Fishman Island.

Additionally, the Red Line is the location of the Reverse Mountain, a unique mountain that connects all four seas, allowing ships to travel between them.

Overall, the Red Line is a crucial aspect of the world of One Piece, serving as a major plot point and setting the stage for many of the story's events.