The Empire of a Thousand Worlds began in 11200 BG, when humanity extended to some one thousand interstellar planetary colonies (it's also possible that the figure "thousand" is symbolical, and simply signifies "a great number"). This interstellar confederation was not actually an Empire (and was considered one merely in name only), since the Imperial power was so diffuse as to be nonexistent. A rebellion, however, destroyed the Imperial Seat of Ceres in 11105 BG, and started the Age of Pretenders. The Empire was eventually reunited as the Empire of Ten Thousand Worlds by Ladislaus the Great.