Kaitain was the Imerpial Capital of the Corrino Empire. It became the capital when the Imperial Seat was moved from Salusa Secundus. Salusa became the Emperor's prison planet.
When the Atreides wrested the Empire from the Corrinos in In 10,196, the Imperial Capital moved from Kaitain to Arrakis, where it remained until the death of Leto Atreides II approximately 3500 years later.