The Province of Cathenau, or Katenyu, is a province of the Gwenithen Empire, which borders Gwenith itself to the Northwest, Maschenya to the Southeast, Enlyll to the West, and Akerrya to the Southwest. Its capital is at Fainair, though the largest city is Zheya. Cathenau is the split in half by the River Savehn (Mas. River Ismal), devided into a largely Gwenithen, Versatian North, and a largely Maschenen, Nischali South. This river boundary serves as the edge of the Lanecyu Dominion,
Following the arrival of the Proto-Gwenitho-Arenians into the Juran Peninsula, a group of Proto-Gwenithens settled in what would become Cathenau. However, unlike their compatriots within Gwenith proper, the Cathenans adopted a governance model based on homesteads, similar to the Proto-Arenians, unlike the City-states of Gwenith. The part of the Cathenau between the River Lein and the River Savehn was settled relatively heavily, while the region to the south of the Savehn was largely ignored.
When the Maschenens arrived on the Peninsula, and began the Maschenen Acquisitions, they conquered all of Cathenau to the River Lein, where they encountered the unified armies of Gallent and Laventeryn, the twin cities of the Riverlands and were forced to stop their advance.
The Maschenens then began settling southern Cathenau with Maschenens, who quickly became by far the largest population in the region, even as they largely left the northern half alone, except for collecting taxes.
Later, the now unified Gwenith reconquered the whole of Cathenau, incorporating it as a province of the Empire. When Maschenya joined the Empire with the Oath of Iron, however, the southern half of the province was incorporated into the Lanecyu Dominion, leading to a complex situation where the Throne-appointed governor must collaborate with the Grand Council of Maschenya on certain matters concerning the southern half of the province, and, while Versatian proselytizing is allowed in the north of the province, it is forbidden in the south by the Two Religions Policy.