The Four Thrones of Cron were the territories comprising Cadinth, Chandaar, Raxus Prime, and Desevro. The first three were conquered by Xer VIII, with the last becoming a part of Xim's Empire.
Sources
Xim Week: The History of Xim and the Tion Cluster on Hyperspace (article) (content removed from StarWars.com and unavailable)
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