""Gnosticism in the Middle Ages"" is a book written by John Yarker that explores the history and development of Gnosticism during the medieval period. The author delves into the origins of Gnosticism, its beliefs and practices, and how it evolved over time. Yarker also examines the influence of Gnosticism on various medieval religious movements and sects, including the Cathars, the Templars, and the Rosicrucians. The book provides a detailed analysis...