The Union of Florence and its rejection by the Church is the most important event in the relations between the Orthodox East and the Latin West. The only participant in the Florence Council (1439) who defended the truth of Orthodoxy to the end was Saint Mark of Ephesus. The book by Archimandrite Ambrose (Pogodin) introduces the reader to the history of the Ferraro-Florence Council and contemporary events, the life and works of Saint Mark of Ephesus, as well as unique theological discussions about the purifying fire, the procession of the Holy Spirit and the Creed. The book is intended for all those interested in the life of the Church, the teachings of Orthodoxy and Latinism, historians and philosophers. The first edition was published in a small print run in the USA in 1963