This volume is the third of a series of works sponsored by the Duke-University of North Carolina Southeastern Institute of Medieval and Renaissance Studies. It presents the public lectures delivered by Senior Fellows at the third session of the Institute held in Chapel Hill during the summer of 1967. Originally published in 1968. A UNC Press Enduring Edition -- UNC Press Enduring Editions use the latest in digital technology to make available again books from our distinguished backlist that were previously out of print. These editions are published unaltered from the original, and are presented in affordable paperback formats, bringing readers both historical and cultural value.