Geometron Pentagon
The seat of the Geometrons' government in the Euclidean Plane was the Pentagon.
It was where the council of six Geometrons at the pinnacle of their society deliberated and drafted laws, kept safe by the highly-trained Official Pentagon Guard. (PROSE: The Euclidean Plane)
The Pentagon also had a forbidden wing housing a library of knowledge about other dimensions which the Geometrons wished to suppress. The Pentagon existed by 1984, when Arganthone-056 participated in a Scarlet Wings mission which involved breaking into it. (PROSE: The Time of the Toymaker)
In 2019, after the Cupid Homeworld was rendered temporarily uninhabitable by an infestation of magical rabbits, the Crew of the Copper-Colored Cupids sought asylum in the Euclidean Plane, with the Copper-Colored Council of Elders walking “humbly” into the Pentagon, waving a white flag. (PROSE: Magic Trick)