Historians of political development in the High Middle Ages often focus on the late twelfth and early thirteenth centuries as the generations in which monarchy finally triumphed over aristocracy to create a monopoly on governing institutions in western Europe. However, it was precisely in this period that Simon of Montfort emerged from his modest forest lordship in France to conquer a principality stretching from the Pyrenees to the Rhône. A remarkable ascendancy in any period, it is perhaps especially so in its contrast with the accepted historiographical narrative. Nonetheless, Simon has been largely overlooked on his own terms, especially by English historiography. Despite the numerous works over the course of the twentieth and twenty-first centuries devoted to the Albigensian Crusade, only a handful of biographies of Simon have been published, none of which are in English. Furthermore, those French works dedicated to his life have been little more than narrative retellings of the Albigensian Crusade from Simon's perspective, with an introductory chapter or two about his family background, participation in the Fourth Crusade, and life in France. French domination of the historiography has also prevented any deep exploration of Simon's English connexions, chiefly his inheritance of the earldom of Leicester in 1206. The substantial inquest regulating this inheritance awaits publication by David Crouch, but at least forty other acts from Simon's life remain unedited, despite increased interest in the Albigensian Crusade and several having been catalogued for over a century. Though one of the aims of this thesis is to correct the lack of Anglophone attention paid to this seminal figure of the early thirteenth century, a biographical study of Simon has consequences beyond the man himself. The inheritance of his claims to the Midi by the French Crown after his death means that his documents survive in a volume uncharacteristic of a baron of his station. The dedicated narrative history of his career provided by Peter of Vaux-de-Cernay's Hystoria albigensis is likewise the most intimate prose portrait of a comital figure available from the period. Thus Simon's life is perhaps the best recorded of his contemporary peers, offering a rare insight into the priorities and means of a baron's administration of his lands and leadership of a crusade. Moreover, despite the supposed triumph of monarchy during his lifetime, Simon's meteoric career took place largely outside of royal auspices and sought crowned approval for its gains only after the fact. Simon's experience was certainly exceptional, both in itself and in the volume of its narrative and documentary records, but it nevertheless provides a challenge to an uncomplicated or teleological understanding of contemporary politics as effectively national affairs directed by kings. Rather than spend his life in the train of one particular king, as did his contemporaries William the Marshal or William of Barres, Simon's career, in its various geographical manifestations, saw him in the lordship of three different Crowns: France, England, and Aragon. Though his relations with the first of these were almost entirely amicable - if not always harmonious - he was more often in open conflict with the latter two. As a crusader, Simon was also subject to a fourth lord, the pope, for the major events of his career. But even while executing papal mandates, Simon at times came into conflict with the distant will of Rome. However, none of these lords successfully prevented Simon's ascendancy. Angevin and Barcan influence in the Midi was drastically handicapped by the Albigensian Crusade, in the latter case, definitively. And while popes may have disagreed with some particulars of Simon's prosecution of the crusade, he remained their best hope for curbing the threat of heresy. One reason for Simon's success in the face of opposition was his ability to exploit the margins of monarchical authority, retreating from his obligations of fidelity to lord in favour of another, thus presenting himself as a legitimate actor while interfering with the designs of a nominal superior. Such independence, however, required alternative bases for his own power that could not be found in the largely rhetorical refuge offered by a distant overlord. In the absence of support from above, Simon worked to cultivate relationships with his social peers and the lesser French nobility. Notably, however, outside of his immediate family, adherence to his cause more often came from his socially inferior neighbours and those with common spiritual devotions than from his wider kinship network. His extended family, of roughly equivalent social standing to himself, were more interested in following the French king in his campaigns to consolidate royal power than investing deeply in Simon's crusade. However, those with similar ideological concerns or dependent on his success saw in Simon a charismatic and effective leader worthy of their allegiance. For Simon himself, the crusade was animated by the programme of reform advocated by the Cistercians and certain Parisian theologians. His context was permeated by the reformers, especially in his close connexions with the abbey of Vaux-de-Cernay. Concerns about just war, the liberation of the Holy Land, ecclesiastical liberty, sexual morality, and the purgation of heresy espoused by Cistercians and schoolmen were reflected in Simon's career. He was more than a simple cipher for ecclesiastical priorities: his campaigns and government were ambiguous in their attitude toward mercenaries and complicit in the problem of usury. Nevertheless, Simon's crusades to both Syria and the Midi demonstrated a remarkable dedication to building a Christian republic according to the vision of the reformers. But Simon was not always a crusader, and the majority of his career - though not the majority of its records - took place in his ancestral lands in France. Though his time in the shadow of Paris does not offer the same salient examples of baronial independence as his conquest of the Midi, it does provide a crucial glimpse at the ordinary exercise of aristocratic government on a more intimate scale. His forest lordship furnished lessons of administration that would prove relevant to his rule in the Midi, such as the diplomatic projection of authority, the value of seigneurial continuity, the economic benefit of thriving towns, the necessity of an intensively participating chivalric following, and the advantage of wide ecclesiastical patronage. Similarly, Simon's brief seisin and subsequent disseisin of the honor of Leicester demonstrated the fragility of his power when many of these elements were lacking. In addition to abstract lessons of governance, his northern lands also provided the financial backing necessary for at least the initial phases of his crusading career. Thus Simon's lordship in France and England, though not nearly as autonomous as in the Midi, is far from irrelevant to his later manifestations of independence: it rather informs his later government and even made it possible.

The humanist Biondo wrote three different narratives of the Fourth Crusade aimed at establishing the legitimacy of western claims to lands in the east. Biondo had played an integral part in the ephemeral reunification of the Greek and Latin Churches at the Council of Florence in July 1439. Biondo blamed the Greeks for the failure and thus did not mourn the loss of their empire to the Ottoman Turks in 1453. However, Biondo did urge several states in the Italian Peninsula to set out en mass to fight the Turks. He viewed the fall of Constantinople as an opportunity for the Latin West to reestablish its rightful empire in the east. He explicated this opinion in at least two different treatises dedicated to rulers shortly after the fall of the ancient city. To Alfonso of Aragon, Biondo argued that the King could establish a peaceful and prosperous extension of his maritime holdings to include a fallen empire with no legal ruler. To the Venetians, he presented the Fourth Crusade as a glorious victory that established their legal claim to rule the now-lost remnants of the Byzantine Empire. Biondo shaped his source material of the Fourth Crusade into an historical narrative that made this primary argument and urged powerful rulers in the Italian peninsula to take back what was rightfully theirs.