The celebrated life of Charlemagne (Vita Karoli Magni Imperatoris, circa 830) by Einhard was matched not long afterward by two Latin prose lives of his son and successor, Louis the Pious; one was written by Thegan, a cleric who was probably from Trier, and the other by an anonymous writer known from one passage in the work as the Astronomer. As historical records of the age, these works go together with a lengthy historical poem by Ermoldus Nigellus, De rebus gestis Ludovici Pii (On the Deeds of Louis the Pious, circa 827), and the first part of Nithart's Liber Historiarum (843).

Thegan (also known as Theganbert and Degen) seems to have been a suffragan of noble birth in the diocese of Trier. He was celebrated in verse as a man of great knowledge by Walahfrid Strabo, who edited his work and corrected the Latin, which was grammatically questionable in places; it...