Founded by the powerful Guelph rulers in the eleventh century as the burial place for their family members, Weingarten Abbey became one of the wealthiest monasteries in Germany in the High Middle Ages, and its fame spread quickly due to the precious relic of Christ's blood that it possessed. A dramatic turn of events took place in 1215 when a fire ravaged the monastery, prompting massive rebuilding and increased book production. In this climate of intense structural and spiritual renewal, the Weingarten sacristan, named Hainricus, commissioned a luxury mass book that he had marked an unprecedented six times with his portrait. As the first comprehensive study of this remarkable manuscript, this dissertation examines what information this liturgical book and its decoration conveys about Weingarten, and about its donor and his personal concerns.

Chapter 1 surveys the complex history of Weingarten Abbey, focusing on the Holy Blood and local monastic illuminators' response to its presence. Chapter 2 examines the extraordinary physical aspects of Morgan 711, including its jeweled, metalwork binding, the silk curtains that cover its illumination, and the colorful embroidered parchment repairs that accent its pages. This chapter also surveys the book's textual contents, discovering nuances that reflect the liturgical concerns of Weingarten and Hainricus Sacrista. Chapter 3 addresses the two cycles of full-page miniatures in the manuscript with their focus on the Apocalypse and on the Virgin Mary as a model for achieving salvation. Chapter 4 explores the illumination imbedded within the text, namely the numerous decorative initials, which create visual narratives for certain feasts when viewed throughout the course of the mass. Chapter 5 investigates the identity of Hainricus Sacrista, examining images of the monk prostrate at the feet of the Virgin Mary and John the Evangelist, and inserted into Apocalypse scenes. This thesis argues for the manuscript's potential as a private devotional book designed to insure the salvation of its donor when he used it during the performance of the mass.