In his sermon On the Ruin of Britain (DEB), traditionally supposed to have been written in the 540s but more realistically at any time between the late fifth and mid-sixth century, Gildas included a political narrative (chapters 4–26). After an introductory chapter (chapter 4), this falls into four sections: a ‘Roman section’ dealing with the conquest of Britain (chapters 5–6); a ‘Christian ‘section’ detailing the evangelisation of the island (chapters 8–12); a ‘northern section’ relating Scottish and Pictish assaults after the Roman departure (chapters 13–21); and an ‘eastern section’ recounting Saxon attacks (chapters 22–6).

Gildas begins his ‘northern section’ by describing the departure of the legions under the tyrannus Magnus Maximus, leaving Britain to suffer Pictish and Scottish attacks. The Britons appealed to Rome. A legion was despatched and built a turf wall to defend the island from attack from the north. This did no good so, after a second appeal, another force was sent, constructing a second, stone wall and instructing the Britons about military defence. This was also to no avail; the barbarians seized the north of the island and ravaged Britain from sea to sea. Eventually the Britons wrote to Aëtius, the military commander in Gaul. In the famous letter, ‘Groans of the Britons’, Aëtius was told how the Britons were driven by the barbarians into the sea and thrown by the sea back to the barbarians. They thus had a choice between two forms of death: drowning or having their throats cut.