This is the first full translation of Marino Sanudo Torsello's Secreta fidelium Crucis to be made into English. The work itself is a piece of crusading propaganda following the fall of Acre in 1291, written between 1300 and 1321, but it includes much of historical relevance along with interesting observations on the early history of Jerusalem and the Crusader Kingdom. The translation is based upon the text edited by Jacques Bongars in 1611. There is an introduction that contextualises the book, its author, his sources and his audience. The notes provide essential information to clarify internal textual references and allusions, as well as the role of Biblical references in Sanudo's grand design. The index is designed to make this detailed text usable and accessible. In this, his major work, Sanudo advocated the conquest of Egypt as the means to regain Jerusalem for the Latins and worked through his points with considerable detail alongside references to 13th-century Mediterranean history, especially involving Louis IX of France and Charles of Anjou, king of Naples. Books I and II give considerable detailed discussion of the concept, plan and costs of his proposed crusade. Book III provides an outline history of the crusades and the crusader states. It is derived from a wide-reading of other sources especially of William of Tyre, and, for events after 1184 on the Eracles, the letters of James of Vitry, and Sanudo's own experiences in the east. Throughout, the work contains a staggering amount of cartographical, ethnographical, geographical, and nautical information, as well as numerous unique insights into historical events and personalities of the late 13th century, not only in Outremer but in Western Europe.