What did ancient Christians and pagans believe makes the unity of the nations? Just as he began serving as a major adviser at the Second Vatican Council in 1962, Joseph Ratzinger (the future Pope Benedict XVI) studied this question in lectures delivered at Austria's University of Salzburg. These lectures, originally published in German, are now made available in English in this volume. According to Ratzinger, pagan Rome said the Empire was the ""cosmopolis"" which united the world. The church affirmed the goodness of the world, and acknowledged the proper role of the state. But Christian...