From the original French book by the author, titled Histoire de la philosophie ancienne et médiévale (published by Grasset, Paris 1998), a first part of ancient philosophy up to Clement of Alexandria and Origen had been translated by Exandas publications. This book presents the continuation, starting with the thought of Plotinus and his students, as well as the Fathers of Christianity. It follows the study of Greco-Roman polytheistic thought, up to the closure of the Neoplatonic school of Athens by Justinian, and the exploration of the Christian Neoplatonism of Dionysius the Areopagite, Maximus the Confessor, and John of Damascus, before the detailed development of five centuries of medieval thought in many aspects. The research concludes with the thought of Plethon, who returned to a renewed form of Platonic philosophy and simultaneously inaugurated Renaissance philosophy. To clarify this historical odyssey of thought, the author used a new reading method, which explores the historicity of philosophy by highlighting thinkers, some of whom maintained their presence through various timeless transformations at the expense of many others who were forgotten either due to ignorance or indifference, or even because of the loss of their works due to natural, climatic, and technical phenomena or religious or ideological pretexts. This multifaceted historical perspective mainly highlights the philosophies that prevailed either by choice or due to circumstances, with the influence mainly of Platonism and Aristotelianism. Thus, in the promotion of certain themes by exclusively referring them to the unilateral ontology, which was mainly established by Thomas Aquinas in the 13th century, the philosophical narrative of the book additionally emphasizes historical complexity, incorporating on the one hand mythical approaches and mysticisms, and on the other hand the enological and agathological practices of metaphysics, which defined the multidimensional historicity of European thought.