One of the barbarian Germanic tribes who attacked Rome in the fifth century, sacking the city in 455. They also ravaged Spain and North Africa, conquering the latter and ruling it from 439 to 534, when they were conquered by the Byzantine Empire.
The Vandals flourished in a time contemporary to Arthur, and Jean D’Outremeuse says that Arthur subjugated them.
See also
Roman Empire | The Legend of King Arthur
Source
Ly Myreur des Histors | Jean D’Outremeuse, c. 1350