Riyona was an ancient empire that stretched north of the Sern River in Timandra. Its fall (roughly a thousand years before the Moth saga begins) marks the beginning of the common Timandrian calender.
Riyona stretched across a vast area roughly analogous to the current kingdoms of Arden, Verilion, Mageria, and Orida. All those four kingdoms currently speak dialects of the old Riyonan language.