Gesta Hludowici Imperatoris

Thegan of Trier (or Degan of Treves) (before 800 – ca. 850) was a Frankish Roman Catholic prelate and the author of Gesta Hludowici imperatoris which is a principal source for the life of the Holy Roman Emperor Louis the Pious, the son and successor of Charlemagne.

Very little is known of Thegan's life; he appears to have come from a noble Frankish family in the middle Rhine-Moselle region. He may have been educated at Lorsch. All that is certain is that by 825 he was auxiliary bishop of Trier and probably praepositus of the monastery of St. Cassius in Bonn. He was also a warm friend of Walafrid Strabo, who was the earliest editor of Thegan's Gesta and divided it into chapters, just as he did with Einhard's Vita Karoli. Walafrid also gave it the name by which it is known: Gesta et Laudes ("Deeds and Praise"), which he mentions in his prologue.

Some poetry and a single letter from Thegan survive. This letter is written to one Hatto who was a count in the Rhine region of Kreuznach, and an important broker in the effort to reconcile Louis the Pious with his son Louis the German in the mid-830s. This concern to promote accord between Louis and his son is similarly evident in the Gesta.

Thegan died between 848 and 853.

Thegan wrote his history of Louis the Pious, translated as "The Deeds of Emperor Louis," in 836-7. The text is a narrative in unpolished Latin, as judged by the standards of the day, written with hortatory intent and based on personal knowledge and communication with friends. Prefaced by a brief prologue by Walafrid Strabo, the Gesta begins with an account of Saint Arnulf of Metz, describes the vicissitudes of the brothers of Louis and gives a more detailed account of Louis' reign during the years 814-835. The later narrative is probably a continuation by another author.

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