For various kindnesses, courtesies, and encouragements given at critical points along the way, I would like to thank, William Durfee, Dorothy M. Habel, Hellmut Hager, T. Kaori Kitao, Thomas Kren, William MacDonald, Peter Murray, Mary Myers, Ursula F. Pace, Valentino Pace, John Pinto, Nan Plummer, Michael Stoughton, and my first teacher of Baroque architecture, Nathan Whitman. Special thanks must also go to Tod Marder whose careful reading of the entire manuscript led to improvements in a number of factual and interpretive passages. In addition, I would like to acknowledge the assistance given by the staff of the Bibliotheca Hertziana, Rome, Kevin Wilson, who drafted the ground plans, and those who had a share in printing my uneven photographic negatives -- Elmont Abbot, Linda Callahan, Thomas Jacob, and Michael Zide. I am also sincerely grateful to the Samuel H. Kress Foundation which funded the printing of those photographs and the drawing of the ground plans, and to the trustees of Mount Holyoke College, whose repeated Faculty Grants assisted my research in a number of important ways. Finally, a personal ringraziamento must go to my wife, Wendy Watson, for her unflagging encouragement and assistance throughout all phases of the project. Her special flair for diverting the attention of suspicious or loquacious building custodians made visits to countless monuments more profitable and enjoyable than they otherwise would have been.