One Piece Ikari no Kecchaku! Red Line o Norikoero! (TV Episode

Impel Down Arc, One Piece Wiki

Warship Island Arc, One Piece Wiki

Red line is based on the Paris meridian and One piece could refer to a legendary treasure hidden in France : r/OnePiece

Where is Red Port located in One Piece?

World, One Piece Wiki

How the red line was created Theory : r/OnePiece

One Piece Wiki Complete One Piece Encyclopedia

For those who think Kaido got massively stronger after his 40's

OC] Destruction of the Red Line [1044+ spoilers] : r/OnePiece

Fish-Man Island Arc, One Piece Wiki