MÄESALU, Mihkel. A Crusader Conflict Mediated by a Papal Legate: The Chronicle of Henry of Livonia as a Legal Text. The Medieval Chronicle. 2013, roč. 8, s. 233–246. Dostupné online [cit. 2023-05-06]. ISSN1567-2336.
BRUNDAGE, James A. The Thirteenth-Century Livonian Crusade: Henricus de Lettis and the First Legatine Mission of Bishop William of Modena. Jahrbücher für Geschichte Osteuropas. 1972, roč. 20, čís. 1, s. 1–9. Dostupné online [cit. 2023-05-06]. ISSN0021-4019.
MÄESALU, Mihkel. A Crusader Conflict Mediated by a Papal Legate: The Chronicle of Henry of Livonia as a Legal Text. The Medieval Chronicle. 2013, roč. 8, s. 233–246. Dostupné online [cit. 2023-05-06]. ISSN1567-2336.
BRUNDAGE, James A. The Thirteenth-Century Livonian Crusade: Henricus de Lettis and the First Legatine Mission of Bishop William of Modena. Jahrbücher für Geschichte Osteuropas. 1972, roč. 20, čís. 1, s. 1–9. Dostupné online [cit. 2023-05-06]. ISSN0021-4019.