Marineford was the island of the base of operations for Marine Headquarters, where now the Marine Base G-1 is situated. It is where former Fleet Admiral Sengoku and three other admirals resided, along with many vice admirals and lower officers when they weren't assigned to another base. The city surrounding Marineford was inhabited by the families of Marine soldiers.

It is situated near the Sabaody Archipelago, and laid directly next to Mariejois on the Red Line. The only safe way to reach Marineford is through the Gates of Justice. However, after the Battle of Marineford, the location of the Marine Headquarters base of operations was exchanged with that of Marine Base G-1.