Though published in 1961, this survey of medieval European history is really quite a good little book. Again, I find that non-fiction written before, say, the 1980s, has a wonderful writing style that makes it much easier to read than non-fiction written today. This is not merely a chronological listing of facts, but an emotive description of a world brought to life.
Heer's argument is that the earlier Middle Ages - from about the late tenth century to the twelfth century - was an "open" society: intellectualism flourished, religion was explored and sometimes even questioned, dialogue and disputation occurred frequently and respectfully between the Muslim, Christian, and Jewish worlds. As time went on, however, the Catholic Church sought to aggrandize its own power, and used censorship, fear, and intolerance as its weapons.
Heer's book is filled with wonderment at the richness of life during this time period. Religious mysticism, courtly love, political machinations, all are discussed both with a depth and brevity befitting of his goal and the length of the book. There is, however, little discussion of the "average" people's existence, beyond their experience of a distinctly rural, half-pagan Christianity. As a general survey of a time period, though, Heer is really quite thorough, and his writing is exciting and easy to read. If only modern non-fiction writers could evoke such feeling as those from the past were able to.
For my own use, documents Heer mentions that I want to check out: Bel Inconnu by Renaut de Beaujeu, Collection of Histories by Rashid al-Din, the Havamal.