Gildas was a sixth-century British monk and historian, known for his work "De Excidio et Conquestu Britanniae." This text provides a valuable account of the history of Britain during the post-Roman period, detailing the decline of Roman influence and the subsequent invasions by various groups, including the Saxons. In his writings, Gildas emphasized moral lessons and the need for spiritual reform among the leaders of his time. His work is one of the earliest historical sources about Britain and offers insights into the social and political challenges faced during the early medieval period.