How did the Breton language arrive in Brittany?

The Breton language was introduced to Armorica—the region now known as Brittany—during the 5th and 6th centuries CE.1

The language arrived via migrants from southwestern Britain who crossed the English Channel to seek refuge from the Anglo-Saxon invasions. As these settlers established colonies in the northwestern part of the Armorican peninsula, they brought their Insular Celtic tongue with them, which eventually became firmly established in the region. This migration was so significant that the area subsequently derived its name, Brittany, from these British settlers.123