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Julia Knödler (2010), "Wassenberg, Battle of", in Clifford J. Rogers (ed.), The Oxford Encyclopedia of Medieval Warfare and Military Technology, translated by Duane Henderson, Oxford University Press.
Martin Clauss (2010), "Cologne, Siege of (1205–1206)", in Clifford J. Rogers (ed.), The Oxford Encyclopedia of Medieval Warfare and Military Technology, translated by Johanna M. Baboukis, Oxford University Press.
