The region that is now Belgium was part of the larger region known as Gallia Belgica by the Romans, and was inhabited by Belgae (a mix of Celtic and Germanic peoples). This area was inhabited by several Celtic tribes before the Roman conquest in the first century BC. However, during the fourth and fifth centuries AD, significant changes took place due to the decline of the Western Roman Empire and the arrival of Germanic tribes.
By the fourth century, the Roman Empire was facing numerous challenges, including invasions and internal strife. In 406 AD, Germanic tribes, including the Vandals, Alans, and Suebi, crossed the Rhine River and invaded Gaul, which included present-day Belgium. These incursions weakened the Roman control over the region.
In the late fourth century, the Roman Empire faced further troubles with the invasion of the Huns led by Attila. To counter this threat, the Roman general Aetius (Agitius) formed an alliance with some of the Germanic tribes, including the Salian Franks, who settled in the northern parts of Gaul.
During the fifth century AD, the Roman authority in Gaul gradually crumbled. In 451 AD, the Battle of the Catalaunian Plains (aslo known as the Battle of Chalons) took place near present-day Châlons-en-Champagne in France. It was a major conflict between the Roman forces led by Aetius and the Huns led by Attila. This battle marked a turning point as it halted the Hunnic advance into Western Europe.
In the aftermath of the Roman collapse, various Germanic tribes established their presence in the region. The Salian Franks, under the leadership of Clovis I, gradually expanded their control and established the Merovingian dynasty. Clovis I, who reigned from 481 to 511 AD, became the first King of the Franks and united many of the Frankish tribes.
This was a part of Arthur’s empire.