Istrium

Istrium is a mountainous region in eastern Orithea, with the Cesynian Plain to its west, the Plain of Urem to its north, and the Thiatian peninsula to its south. To the east, it is separated from Ekhroa by the Bay of XXXXXXX. The line marking Istrium's southern edge (and the northern border of Thiatia) is generally considered to be the Adomos River valley; the valley floor is long, sinuous strip of low-lying country that runs for hundreds of miles between the highlands of the two regions.
The entirety of Istrium is a part of the Kirdan Empire, although as a mountainous peripheral region, imperial control there is often a bit shakier than it is down on the Plain of Tethas. The Istrian highlanders have always chafed under Kirdan rule, and there have been several localized uprisings over the years.