The Fifth Crusade's losses are recorded in narrative form, the long siege of Damietta and the crusader army's destruction during its retreat up the flooded Nile, but no historian has converted those narratives into a bounded casualty estimate for the campaign.
What would resolve this A military historian's accounting of losses at Damietta and during the Nile retreat combined into one campaign total, or a demographic study of Ayyubid Egypt's war losses in the period.
OpenCrusading history, medieval military history.Christopher Tyerman, God's War: A New History of the Crusades