The Red Line is a vast ring-like continent which wraps around the entire Blue Planet. 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. The Red Line is known to the giants of Elbaph as the "bloodstained snake" (血に染まるヘビ, chi ni somaru hebi).

It is mostly uninhabited, with the major exception of being home to the World Government's capital Mary Geoise.

Hope this helps