This book has been written thanks to the help and support of many people. I would like to thank Professor Roman Michałowski for including me in his research team and for his valuable remarks. I recall with gratitude Professor Henryk Samsonowicz ( † 2021) for his kindness and for the discussions during the Medievalist Doctoral Seminar at the Institute of History, University of Warsaw, where I was able to present successive chapters of the book. I am grateful to Krzysztof Skwierczyński, Grzegorz Pac, Michał Gronowski, and Piotr Węcowski for their advice and assistance in obtaining the necessary literature. My thanks go to Dr Anna Adamska from University of Utrecht for consultations and words of encouragement while preparing the English version of this book. I owe most to Professor Karol Modzelewski, my Master, who always supported me and always believed in me and who passed sadly away in 2019, before the translation was finished. I would like to extend special thanks to my family for bravely enduring the difficult period when I was writing and translating the book. newgenprepdf xi v 1 Chapter 1 inTroducTion 8 Duby, La société aux XI e et XII e siècles, see also Bougard, "Genèse et reception"; nearly twenty years later Duby abided by his main theses in Duby, "Lignage, noblesse et chevalerie," 803-23. The role played by Duby and the discussion surrounding the breakthrough in social structures in the eleventh century are analyzed by Bisson, "Nobility and Family." 9 Duby, Le chevalier, la femme et le prêtre. 10 For a discussion of the arguments of the critics, including Friedrich Prinz, Karl Bosl, Wilhelm Störmer, and Karl Leyser, see Freed, "The Counts of Falkenstein," 1-11. 11 The 1990s were marked by the publication of numerous studies revising the established views on the "feudal revolution" of the eleventh century. The most important among them was the discussion on the pages of the Past and Present journal in 1994-1997. Its participants included Thomas Bisson, Dominique Barthélemy, Stephen D. White, and Chris Wickham. See also Bagge, Gelting, and Lindkvist, eds., Feudalism: New Landscapes of Debate.25 Among the studies devoted to relations among siblings published in recent years in social sciences the one that can be useful as an introduction to the topic is a study by the French sociologist Buisson, La fratrie, creuset de paradoxes, because of its cross-sectional nature and the author's sensitivity to historical contexts; see also Coles, ed., Sibling Relationships; Alber, Coe, and Thelen, eds., The Anthropology of Sibling Relations; Buchanan and Rotkirch, eds., Brothers and Sisters.26 The scholar who has studied the question of siblings in history, especially in the late Middle Ages, most intensely is Didier Lett. See Histoire des frères et soeurs, a revised version of the study: Frères et soeurs: Histoire d'un lien. See also important collections of studies: Godeau and Troubetzkoy, eds., Fratries: Frères et soeurs; Miller and Yavneh, eds., Sibling Relations and Gender; Johnson and Sabean, eds., Sibling Relatio...