Dei patris immensa
Dei patris immensa was a letter written by Pope Innocent IV to the Mongols (the Pope also wrote other letters to the Mongols, which are known as Cum non solum and Viam agnoscere veritatis). It was written on March 5, 1245, was an exposition of the Christian faith, and urged Mongols to accept baptism. It was intended to be carried by the Franciscan friar and papal envoy Laurentius of Portugal. However, nothing more is known about Laurentius' embassy, and it is possible that he never actually left.
Ecclesiastical letters are generally named by modern scholars, according to their incipit, or beginning. This letter starts with similar language to the two other letters, Viam agnoscere veritatis and Cum non solum. The letter starts, "...regi et populo Tartarorum viam agnoscere veritatis. Dei patris inmensa benignitas humani generis casum, quod primi hominis culpa corruerat, ineffabili respiciens pietate..." It has been referred to by different names, such as "Dei patris inmensa", "Dei patris immensa", and "Verbum agnoscere" from different scholars choosing different parts of the incipit to refer to it.
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- Monumenta Germaniae Historica; Epistolae Saeculi XIII: E Regestis Pontificum Romanorum, ed. Karl Rodenberg (Berlin, 1887), Vol. 2, No. 102, p. 72. 
- Gregory G. Guzman, "Simon of Saint-Quentin and the Dominican Mission to the Mongol Baiju: A Reappraisal" Speculum, Vol. 46, No. 2. (April., 1971), p. 243.
- Sandra Brand-Pierach, Ungläubige im Kirchenrecht, Text of the letter p.174 
- Dawson, Christopher (1980), Mission to Asia, University of Toronto Press in association with the Medieval Academy of America, ISBN 0-8020-6436-1, English translation of text of the letter
- Jackson, Peter (2005), The Mongols and the West, 1221-1410, Pearson Education, ISBN 0-582-36896-0
- Roux, Jean-Paul, Histoire de l'Empire Mongol, 1993, Fayard, ISBN 2-213-03164-9
- Setton, Kenneth Meyer, A History of the Crusades
- MGH Epp. Saec. XIII, Volume 2, pp. 72-75 (original source documents)
- Grousset, Rene, Histoire des Croisades, III, Tempus, 2006 edition, ISBN 2-262-02569-X
- Rachewiltz, I, Papal Envoys to the Great Khans, Stanford University Press, 1971.
- Runciman, Steven, History of the Crusades, III, Penguin Books, 2002 edition, ISBN 0-14-013705-X