Question: Ambrosius Aurelianus as a war leader of the Romano-British who won an important battle in the 5th century, according to a 6th-century British monk best known for his scathing religious polemic which recounts the history of the Britons before and during what? 
Sentence (from "Ambrosius Aurelianus"): Ambrosius Aurelianus (Welsh: "Emrys Wledig" ; Anglicised as Ambrose Aurelian and called Aurelius Ambrosius in the "Historia Regum Britanniae" and elsewhere) was a war leader of the Romano-British who won an important battle against the Anglo-Saxons in the 5th century, according to Gildas.
Relevant evidence: Yes