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.
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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.