The Octagon was the headquarters of the Secretary of War of the People's Republic of Haven, situated in Nouveau Paris on the planet Haven.

Its architecture included a towering black spire. (HH3)

On December 18, 1914 PD, Secretary of War Admiral Esther McQueen used the Octagon as the command center for her coup against Rob S. Pierre's government. Pierre and most of the Committee of Public Safety were killed or detained in the Octagon by McQeen and conventional assaults proved ineffective at recapturing the building. Oscar Saint-Just ordered General Speer to activate "Bank Shot", a nuclear device planted under the Octagon. The detonation of the bomb destroyed the building and the surrounding area, killing 1,300,000 people. (HHA3.2: N, HH9)

By 1920 PD the Republic of Haven, under President Eloise Pritchart, had rebuilt the facility and the New Octagon was in operation as the Navy's central headquarters. (HH10)