When Charlemagne died in 814 CE, he left behind a dominion and a legacy unlike anything seen in Western Europe since the fall of Rome. Distinguished historian and author of The Middle Ages Johannes Fried presents a new biographical study of the legendary Frankish king and emperor, illuminating the life and reign of a ruler who shaped Europe's destiny in ways few figures, before or since, have equaled.

Living in an age of faith, Charlemagne was above all a Christian king, Fried says. He made his court in Aix-la-Chapelle the center of a religious and intellectual renaissance,...