Who is Severus from The History of the Kings of Britain and what is their importance?

After Lucius' death, Severus is sent to Briton to restore order. He is directly responsible for constructing a wall between Deira and Albany. The purpose of the wall is to prevent Sulgenius from gaining access to the larger population outside of Albany. Sulgenius kills Severus in battle. He was the father of two sons: Bassianus and Geta.