Gwrtheyrnion or Gwerthrynion was a commote in medieval Wales, located in Mid Wales on the north side of the River Wye. For most of the Middle Ages, its rulers operated independently of other powers, but it was sometimes associated with the cantref of Maelienydd and the Kingdom of Powys, and, in the Norman era, with the region known as Rhwng Gwy a Hafren. It is said to have taken its name from the legendary king Vortigern (Welsh: Gwrtheyrn), and for a time was part of an independent regional kingdom.