Arcadia

Arcadia, known also as the Planet of Law, is a hidden Harlequin world situated within the Eye of Terror, in Segmentum Obscurus. No system name or coordinates for it are recorded. It is reached only through the warp and the Webway, and it is guarded by its resident Harlequins. It is distinct from any other world bearing the same name.

Within Arcadia’s canyons lies the Arcadian Librarium, a city-sized archive counted among the largest repositories of knowledge on record. The Tome of Karebennian, consulted by those seeking the Black Library, leads its readers to Arcadia rather than to that destination, making Arcadia a false path toward the Black Library.

Necrons sought to close the portals granting access to Arcadia, a pursuit that brought them to Lorn IV. In the late 41st millennium, Ahzek Ahriman led the Prodigal Sons against the Librarium during the 13th Black Crusade, but did not reach the Black Library by that route.