Brittain

[T]his so famous and farre renown'd great Brittains Monarchy, had at one blowe endured a recouerlesse ruine, beeing ouerwhelmed in a sea of bloud; […]

Source: wiktionary

Henry, by Mary Queen of Scots, had Issue James the Sixth, King of Brittain, by the propitious Grace of the Eternal God, born in a most auspicate and lucky Hour, to knit and unite in one Body of an Empire, the whole Island of Brittain, divided as well in it self, as it was heretofore from the rest of the World, and to lay a most sure Foundation of an everlasting Security, for our Heirs and the Posterity.

Source: wiktionary

Sixtly, That this Realme was diuided into Shires and Counties, and thoſe Shires into Cities, Burroughs, and Townes, by the Bꝛittains.

Source: wiktionary

But since this custome was probably disused before their Invasion or Conquest, and the Romanes confessedly practised the same, since their possession of this Island, the most assured account will fall upon the Romanes, or Brittains Romanized.

Source: wiktionary