Tamm, Marek (2013). "How to justify a crusade? The conquest of Livonia and new crusade rhetoric in the early thirteenth century". Journal of Medieval History. 39 (4): 431–455. doi:10.1080/03044181.2013.833541. S2CID159762394.
Tamm, Marek (2013). "How to justify a crusade? The conquest of Livonia and new crusade rhetoric in the early thirteenth century". Journal of Medieval History. 39 (4): 431–455. doi:10.1080/03044181.2013.833541. S2CID159762394.