Question: King Arthur is a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries AD, the sparse historical background of Arthur is gleaned from various sources, including the writings of Gildas, a 6th-century British monk, best known for his scathing religious polemic titled what?
Answer: De Excidio et Conquestu Britanniae