Home of the Emperor of the known Universe until the reign of Emperor Shaddam IV. After the conclusion of the Arrakis Revolt the capitol was moved to Arrakis in 10196, when Paul Atreides, the leader of the revolt deposed Shaddam IV.
House Corrino had moved the Imperial Seat to Kaitain some 8,709 years before, in the standard year 1487. It is believed that they ruled from Salusa Secundus before that planet was designated as the imperial prison. At this time I do not know where the Corrinos ruled from during the interim between S.S. becoming the prison planet in 388.
(from Dune by Frank Herbert)