The Red Line is a vast ring-like continent which wraps around the entire world. It serves as a border separating the East and South Blues from the North and West Blues on both sides, as well as separating the two halves of the Grand Line.[2]
It is mostly uninhabited, with the major exception of being home to the World Government's capital Mary Geoise.
As its name implies, the Red Line is made of reddish mineral. It runs from southwest to northeast along Paradise, and northwest to southeast along the New World. It is said to go 10,000 meters deep from the surface of the sea to Fish-Man Island at the ocean floor.[3] At the same time, the top of the Red Line is high enough above sea level to be considered impassable. The Red Line is also indestructible, even the power of the Nikyu Nikyu no Mi, which can repel anything at the speed of light, cannot break through it.[4][5] Additionally, the Red Line is like a group of islands connected together. The Red Line that crosses the Grand Line has its own Summer, Winter, Spring, and Fall "islands".[6]
The position of the Red Line.
Red Line islands.
While the continent appears to make it impossible for any boat wishing to cross between the seas or to certain sections of the Grand Line, there are certain pass points at which a ship, or at least the crew, can cross between the Blues. One way is by going up the waterways of Reverse Mountain, typically used by pirates to enter the Grand Line. Another way is by gaining permission from the World Government to pass through the holy land of Mary Geoise, though this route means that a crew would have to leave their ship behind and get a new one on the other side. Finally, a crew could get their ship coated, allowing it to submerge down to Fish-Man Island, allowing them to reach a gigantic hole (though in the grand scheme of things, the hole is actually very tiny) at the bottom of the Red Line that links directly between Paradise and the New World.
Red Line's hole below Mary Geoise.
It is almost impossible to pass over it or under it without using one of the entrances. However, Fisher Tiger managed to climb up to the top of the Red Line with his bare hands to attack Mary Geoise.[7] The whole of Germa 66 was also able to climb over the Red Line, from North Blue into East Blue, using its amphibious snail ships.[8]
It is said that, long ago, before Mary Geoise was built, the Lunarian race lived on top of the Red Line, when it was known to be a "Land of Gods". Their unique attributes are that they have black feathery wings, dark skin, white hair, and the natural ability to generate flames from their body. This race is widely believed to be extinct, and its only known living member is King.[9][10]
The capital city of the World Government, Mary Geoise is located atop the Red Line at the halfway point of the Grand Line where the Red Line and the Grand Line cross. It is directly above Fish-Man Island, which is located in an underwater passageway that cuts through the Red Line.
At each side of the Grand Line, at the base of the Red Line, directly below Mary Geoise, is the Red Port, which has special lifts called Bondolas (ボンドラ,Bondora?) that reach Mary Geoise and allow those who were granted access to cross the Red Line to pass though Mary Geoise.
On the exact opposite side of the world from Mary Geoise is Reverse Mountain, where water from the four Blues flows up the mountain and down into the first half of the Grand Line. The Twin Cape is at the base of the mountain.
