There were two Gaulish chiefs of this name, both leaders of invasions. It is possible that “Brennus” was a title, meaning dux bellorum or “commander-in-chief’ rather than a personal name.
Diodorus Siculus tells us about the second Gaulish King Brennus, who lived in the third century BC:
Brennus the King of the Gauls, on entering a temple [at Delphi in Greece] found no dedications of gold or silver, and when he came only upon images of stone and wood, he laughed at them [the Greeks], to think that men, believing that gods have human form, should set up their images in wood and stone.
The implication is that the more sophisticated Gauls did not think of the gods in anthropomorphic terms and this tallies with their art, much of which at that time did not feature humanoid forms.
It was an earlier Gaulish King Brennus, who was the King of the Senones tribe, who led the Celtic warriors in the sack of Rome in 387 BC. He caused more havoc there than would be seen again until Alaric the Goth descended on the city in the fifth century AD. Brennus demanded his own weight in gold, with the cry, “Vae Victis! ” (“Woe to the defeated!”) He was interested in loot rather than conquest, which was perhaps unfortunate in the longer term, though the Celts remained a force to reckon with in Italy until 295 BC.
BRIDEI
King of the Picts, who reigned from 555 to 584. He is the only British king from the fifth or sixth centuries to be mentioned in a chronicle on the European mainland. Bede describes him as rex potentissimus, “most powerful king,” which suggests that the Picts had their own overking. Bridei, or Brudeus, was a son of Maelgwn, King of Gwynedd, and he was elected king. The Picts would not have chosen an obscure or low-ranking person as their king, and Maelgwn, we know, was an overking. Pictish succession passed through the female line, so it is likely that for him to be eligible for the Pictish throne; Bridei’s mother or grandmother was a Pict. In fact Welsh tradition has it that Maelgwn’s mother was a Pict.
Bridei’s high reputation among the Picts rests on a great military victory won in 560. Gabran, King of Dal Riada, had taken a large area of Pictland and, by defeating him in 560, Bridei won most or all of this land back and once more united the northern and southern Picts.
St. Columba visited him and asked Broichan, his chief magician, to set free his Irish slave girl.
Bridei was eventually killed in 584 during a rebellion of the southern Picts.