Definition of "foederati"

The third part of the vision was more conventional and it concerned lines of native princes descending from tribal leaders, or Roman foederati like Cunedda, or from Cadwaladr the Blessed, last Welsh king to claim over-lordship of Britain, in the seventh century, right down to the death of Llywelyn II in 1282.

[DATE?]: Prys Morgan, The Invention of Tradition, pUnknown