These symbols and rhetoric are used to provide a religious justification and inspiration for a struggle against a religious enemy. Historiography The historiography of the Crusades is concerned with their "history of the histories" during the Crusader period. The subject is a complex one, with overviews provided in Select Bibliography of the Crusades, Modern Historiography, and Crusades (Bibliography and Sources). The histories describing the Crusades are broadly of three types: (1) The primary sources of the Crusades, which include works written in the medieval period, generally by participants in the Crusade or written contemporaneously with the event, letters and documents in archives, and archaeological studies; (2) secondary sources, beginning with early consolidated works in the 16th century and continuing to modern times; and (3) tertiary sources, primarily encyclopedias, bibliographies and genealogies. Primary sources. The primary sources for the Crusades are generally presented in the individual articles on each Crusade and summarized in the list of sources for the Crusades. For the First Crusade, the original Latin chronicles, including the Gesta Francorum, works by Albert of Aachen and Fulcher of Chartres, The Alexiad by Byzantine princess Anna Komnene, the Complete Work of History by Muslim historian Ali ibn al-Athir, and the Chronicle of Armenian historian Matthew of Edessa, provide for a starting point for the study of the Crusades' historiography. Many of these and related texts are found in the collections Recueil des historiens des croisades (RHC) and Crusade Texts in Translation. The work of William of Tyre, Historia Rerum in Partibus Transmarinis Gestarum, and its continuations by later historians complete the foundational work of the traditional Crusade. Some of these works also provide insight into the later Crusades and Crusader states. Other works of note include: Eyewitness accounts of the Second Crusade by Odo of Deuil and Otto of Freising. The Arab view from Damascus is provided by ibn al-Qalanisi. Works on the Third Crusade such as Libellus de Expugnatione Terrae Sanctae per Saladinum expeditione, the Itinerarium Regis Ricardi, and the works of Crusaders Tageno and Roger of Howden, and the narratives of Richard of Devizes, Ralph de Diceto, Ralph of Coggeshall and Arnold of Lübeck. The Arabic works by al-Isfahani and al-Maqdisi as well as the biography of Saladin by Baha ad-Din ibn Shaddad are also of interest. The Fourth Crusade is described in the Devastatio Constantinopolitana and works of Geoffrey of Villehardouin, in his chronicle De la Conquête