|Aegidius I||c. 457-464|
Prior to Aegidius' appointment as magister militum per Gallias by the Emperor Majorian, the territory of Lyonesse was an integral part of the Western Roman Empire proper. For its rulers then, see List of Roman emperors and Praetorian Prefects of Gaul.
Gallia Lugdunensis was conquered in 486 by Clovis I of the Salian Franks, becoming the Neustrian part of the Merovingian realm.
Merovingian rule over Neustria effectively ended with the death of King Dagobert at the Battle of Castras and the dismemberment of his realm. Clovis II was overthrown a few years later by the Visigoths and fled to the Frankish homeland.
Caesarius, a member of the native Gallo-Roman aristocracy, was installed as a client king subject to Spain.
Syagrian Dynasty (restored)
During this time Lyonesse was little more than a client kingdom of Spain. From the mid-8th century onwards it once more came under pressure from the Franks, eventually being conquered by Charlemagne, Holy Roman Emperor.
After the death of Louis I, the Holy Roman Empire was divided and Lyonesse once more became an independent kingdom. The last Carolingian king, Charles IV, ceded the throne to the Norseman, Rollo, in exchange for peace.
Under the Jersiais, Lyonesse briefly entered into a personal union with Arvor and Prydain. Guillaume IV divided his lands between his two sons, with Prydain going to the elder, Aneirin, and Arvor and Lyonesse going to Ambrose II. This allowed Lyonesse to gradually absorb Arvor and eventually annex it.