My SG has suggested biographies of Eleanor of Aquitane and histories on the Cathar Heresy...
Wikipedia lists these sources for Cathars:
^ R.I. Moore's The Origins of European Dissent, and the collection of essays Heresy and the Persecuting Society in the Middle Ages: Essays on the Work of R.I. Moore for a consideration of the origins of the Cathars, and proof against identifying earlier heretics in the West, such as those identified in 1025 at Monforte, outside Milan, as being Cathars. Also see Heresies of the High Middle Ages, a collection of pertinent documents on Western heresies of the High Middle Ages, edited by Walter Wakefield and Austin P. Evans.
^ Emmanuel LeRoy Ladurie's Montaillou: the Promised Land of Error for a respected analysis of the social context of these last French Cathars, and Power and Purity by Carol Lansing for a consideration of 13th-century Catharism in Orvieto.
^ Massacre at Montsegur: A History of the Albigensian Crusade, Zoe Oldenbourg
^ "Caedite eos. Novit enim Dominus qui sunt eis." Caesarius of Heisterbach, Caesarius Heiserbacencis monachi ordinis Cisterciensis, Dialogus miraculorum, ed. J. Strange, Cologne, 1851, J. M. Heberle, Vol 2 , 296â€“8. Caesarius (c) was a Cistercian Master of Novices.
^ Patrologia Latinae cursus completus, series Latina, 221 vols., ed. J-P Migne ), Paris, Vol. 216:col 139
^ Martin, Sean (2005). The Cathars. Pocket Essentials, pp105â€“121. ISBN 978-1904-04833-1.
^ See the Bull of Innocent IV Ad exstirpanda, 1252.
^ Weis, RenÃ©. The Yellow Cross: The Story of the Last Cathars. (Alfred A. Knopf, New York, 2000), 11â€“12.
And on Eleanor of Aquitane:
Eleanor of Aquitaine: Lord and Lady, John Carmi Parsons & Bonnie Wheeler (2002)
Queen Eleanor: Independent Spirit of the Medieval World, Polly Schover Brooks (1983) (for young readers)
Eleanor of Aquitaine: A Biography, Marion Meade (1977)
Eleanor of Aquitaine and the Four Kings, Amy Kelly (1950)
Eleanor of Aquitaine: The Mother Queen, Desmond Seward (1978)
Eleanor of Aquitaine: A Life, Alison Weir (1999)
Le lit d'AliÃ©nor, Mireille Calmel (2001)
"The Royal Diaries, Eleanor Crown Jewel of Aquitaine", Kristiana Gregory (2002)
Women of the Twelfth Century, Volume 1 : Eleanor of Aquitaine and Six Others, Georges Duby
A Proud Taste For Scarlet and Miniver, E. L. Konigsburg
The Book of Eleanor: A Novel of Eleanor of Aquitaine, Pamela Kaufman (2002)
The Courts of Love, Jean Plaidy (1987)
Power of a Woman. Memoirs of a turbulent life: Eleanor of Aquitaine, Robert Fripp (2006)