NIGHTBRINGER | The Arthurian Encyclopedia

Leo I

Reign: 457-474 AD
Leo the Great, Leo the Thracian
Leomyaé, Leomye

Leo I served as the Eastern Roman Emperor from 457 to 474 AD. He sometimes referred to as Leo the Great, although this title is more commonly associated with Pope Leo I.

Roman emperor in the East, reigning at Constantinople from 457 to 474. Emperor of Rome during Arthur’s reign, according to Geoffrey of Monmouth. He supplies the only chronological fix for Arthur – that is, the only clear synchronization with known history outside Britain – that is given by any of the sources up to the time of Geoffrey of Monmouth.

Describing Arthur’s expeditions to Gaul, Geoffrey portrays that country as still belonging to the Empire, or at least claimed by it. However, the nature of the imperial power is ill defined. In the first expedition, Gaul is ruled by the tribune Frollo “in the name of emperor Leo”. In the second, there is an equivocal western emperor, Lucius. But Lucius has a colleague whose imperial status is definite, who is not in Rome but somewhere beyond, and whom Arthur never confronts; and this “real” emperor is still named as Leo, twice. In all three places, he can only be Leo I. Leo II was a child who succeeded him and died almost at once, and there was not another Leo for centuries. Even the allegiance of Frollo could have a factual basis. During the 460s, an interregnum occured when Leo had no western colleague and was sole emperor. Leo commissioned Lucius Hiberius to lead the war against Arthur. After Arthur defeated and killed Lucius, he planned to march on Leo in Rome, but he was recalled to Britain to deal with Mordred’s rebellion.

The naming of Leo, three times, is wholly gratuitous, since he plays no part in the story. Geoffrey’s general methods would suggest that when he wrote of Arthur’s Gallic warfare his imagination was working (however wildly) on records putting British activities in Gaul in Leo’s reign. He has a comparable chronological fix for Vortigern, making his major Saxon dealings coincide with the British mission of Germanus and Lupus, two Gallic bishops whose careers – including their visit to Britain in 429 – are attested by continental records. In that instance, Geoffrey is undoubtedly drawing on older writings, why interest attaches to the Gallic expedition, in Leo’s reign, on the British king known as Riothamus.

Most chronicles drop Leo and make Lucius the emperor of Rome. In the Alliterative Morte Arthure, Leo becomes Lucius’s soldier rather than his superior.

Emperor Leo I | 401-474 AD

Leo I, often known as Leo the Thracian, was born around 401 AD in Dacia Ripensis, a province in the Eastern Roman Empire. He came from humble origins, and his early life is not well-documented. His rise to power began when he joined the Roman army and distinguished himself as a soldier.

In 457 AD, Leo I became Emperor of the Eastern Roman Empire after the death of Emperor Marcian. His ascension to the throne marked a significant moment in Roman history because he was the first Byzantine Emperor who was not of Latin descent. Leo was of Illyrian and Thracian heritage, and his reign is often associated with a shift toward the predominance of Greek culture and language in the Eastern Roman Empire. During his rule, Leo I faced several challenges.

Relations with the Western Roman Empire
The Western Roman Empire was in a state of decline and turmoil, and Leo I had to navigate diplomatic and political issues with the western part of the empire, which was often ruled by puppet emperors controlled by various barbarian groups.

Religious Affairs
Leo I played a significant role in church matters. He supported the Chalcedonian Definition in 451 AD, which defined the orthodox Christian doctrine concerning the nature of Christ. His efforts helped establish the theological foundation for the Byzantine Empire’s relationship with the Church.

Diplomacy with Attila the Hun
In 452 AD, Leo I and Pope Leo I played crucial roles in convincing the Hunnic leader Attila not to invade Italy. Their diplomatic efforts prevented a potentially catastrophic invasion.

Conflict with the Vandals
Leo I faced a major threat from the Vandal kingdom in North Africa. In 468 AD, a major expedition against the Vandals was launched, but it ended in failure, which weakened the Eastern Roman Empire’s position in the western Mediterranean.

Legal Reforms
Leo I implemented various legal reforms during his reign to imporve the administration of the empire.

Emperor Leo I died in 474 AD and was succeeded by his grandson, Leo II. His reign left a lasting legacy in Byzantine history, as he played a key role in shaping the empire’s political, religious, and cultural development during a period of significant transition. His emphasis on diplomacy and his ability to navigate complex geopolitical challenges are notable aspects of his rule.

Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
The Chronicle of Pierre de Langtoft | Pierre de Langtoft, c. 1300-1307
Alliterative Morte Arthure | c. 1400