John, surnamed Prefet John, was son to a king of the Frisii; and, from the austerity of his life, obtained the name of Prefet, or Priest. He attended Charlemagne in his expedition to the Holy Land; but instead of returning with that monarch to Europe, it is pretended that he gained mighty conquests, and founded the empire of the Abyllines, called, from his name, the empire of Prefet John. He is said to have written the history of Charlemagne's journey into the Holy Land, and his own into the Indies; but they are more probably trifling romances, written in the ages of ignorance.