Marineford

Marineford was the main headquarters of the Marines (海軍本部 Kaigun Honbu, Marine Headquarters, Navy Headquarters in FUNimation subs). It is where Fleet Admiral Sengoku and the three Admirals resided, along with many Vice Admirals and lower officers when they weren't assigned to another base. The city surrounding Marine HQ was inhabited by the families of Marine soldiers. Marineford was one of the three great powers, alongside the Shichibukai and the Yonkou.

It is situated near the Sabaody Archipelago, and lied 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 was exchanged with that of Marine Base G1.

Shiki's Assault
Twenty-two years ago, after hearing that the Pirate King Gol D. Roger had been captured by the Marines and would face execution in Loguetown, "Gold Lion" Shiki came to Marineford alone, in his angry refusal to believe the Marines would be able to capture Roger, and killed many soldiers in the process. Vice Admiral Monkey D. Garp and Admiral Sengoku then fought against Shiki together. After a fierce battle between these three men, half of Marineford was reduced to rubble, many were injured or killed, and Shiki was defeated, captured, and incarcerated in Impel Down.

East Blue's Newest Pirate
Shortly after the defeat of East Blue's most powerful pirates at the hands of Monkey D. Luffy, the higher officers here granted him his first bounty of 30,000,000.

Vice Admiral John Giant then announced to every high-ranking officer that the Marines there must be prepared to serve justice with all their might, and that there is no room for cowardice or moral justice.

Over time, Fleet Admiral Sengoku spent his time here, giving orders to lower ranking subordinates, and taking out his fury over Monkey D. Luffy's repeated actions on his grandfather, Monkey D. Garp. The Buster Call that Spandam accidentally activated was also sent from Marineford, taking roughly half-an-hour to arrive at Enies Lobby.

Defending against Whitebeard
Marineford became the site of the war against the Whitebeard Pirates, and the central plaza was where Portgas D. Ace was to be executed. With careful planning from Sengoku, the siege wall plan was set up to surround the pirates while Admiral Akainu melted the frozen ice floor created by Admiral Aokiji, in an attempt to destroy the crew and their allies, as well as Luffy and his recruits from Impel Down. However, thanks to Oars Jr., the rescue party managed to enter the main plaza, but ultimately failed to save Ace from death. Whitebeard tilted the entire island, and launched many shock waves to destroy the Marine Headquarters' main building with his earthquake powers.

Blackbeard Pirates Invasion
The Blackbeard Pirates entered and were seen standing around the execution platform. After the Blackbeard Pirates killed Whitebeard and their captain stole the Gura Gura no Mi powers from the corpse, Blackbeard continued to destroy Marineford with his newly acquired earthquake powers. Aokiji refreezes the ocean to prevent the pirates from escaping. Sengoku retaliates, refusing to let Blackbeard sink the island. Trafalgar Law made his way to the place to pick up the severely injured Luffy, as well as Jinbei, who was carrying the mind-shattered Luffy. As Luffy is taken away, the Red-Haired Pirates arrived, with Shanks blocking Akainu's attack on Coby, who had questioned the moralities of the Marines.

End of the War
After the war was ended thanks to Shanks' intervention, Sengoku is seen sitting on the rubble of the island, which is being rebuilt, and Brandnew coming in to report Impel Down's conditions. As it is being rebuilt slowly, it attracted onlookers and reporters from numerous countries to come watch. It received some further minor damage when Luffy returned with Jinbei and Silvers Rayleigh to ring the Ox Bell 16 times. However, it seems that Aokiji's office suffered only minor damage throughout the war, as he was able to sit in it with Smoker to talk about the latter's reassignment.

Two years time skip
After the Marineford battle, the new Fleet Admiral decided to change the location of the Marine HQ with the G1 branch, which is in the New World, directly challenging the power of the Yonkou. The old Marineford has been rebuilt, with a prominent G1 painted on the side of the building.