The four volume series consists of three volumes which cover general areas and a final volume which provides guidelines for converting history to fantasy campaigns. The volumes are as follows:
Volume I: Arms, Armor, and Warfare of the Middle Ages
--This volume covers the weapons, armor,ships, and tactics of the period.
Volume II: Society and Culture of the Middle Ages
--This volume covers every day life, economics, legal structure, social customs, education, etc.
Volume III: Religion, Magic, and Mythology of the Middle Ages
--This volume covers the extremely blurred line of religion and magic and covers the mythological creatures of
folklore and literature.
Volume IV: The Middle Ages in the Modern World of Fantasy
Or maybe a one volume series with approximately 30-50 pages on the subjects of Volume I, 80-100 pages on society and culture, and 80-100 pages on religion, magic and mythology.