This book has been in preparation for more years than I care to remember. My first duty is to thank successive editors at Cambridge University Press, Bill Davies and Simon Whitmore, for their almost superhuman restraint with an author who must have sorely tried their patience. I hope that they think the wait has been worthwhile. Secondly, I must thank the Leverhulme Trust, which paid for replacement teaching to allow me an entire year's study leave in 2005–6, during which almost all of this book was finally written. This is the second book of mine whose writing the Trust has facilitated: I am genuinely and deeply grateful for their generosity. I must also thank my colleagues, and especially Alan Murray, who ensured that my second-year pupils were in good hands during my absence, and Wendy Childs and Emilia Jamrosiak, who shouldered extra teaching and administration with exemplary grace.

The intellectual debts incurred have been many, only a few of which I can mention here. I am lucky to have access to the Brotherton Library at the University of Leeds, with its outstanding resources in medieval history. I am grateful to the former History librarian Neil Plummer, and the current incumbent Jane Saunders, for their stewardship, and for ordering so many recondite volumes for me and for my pupils. I have also benefited from the kindness of numerous colleagues in Italy, and also France and Germany, especially in sending me copies of books and articles that I might otherwise have missed, or which might have been unobtainable in Britain, and from which I have profited greatly.