From what I've been learning about, the First Crusade. Kedar writes about the many different perspectives of the Jerusalem Massacre of 15 July 1099. The primary sources themselves disagree on many aspects, including the length of time the massacre took (was it only the 15th or was it 15-17th?), the totality of the carnage (ranging from almost to total), what happened to the survivors (were they enslaved?), and how much blood was in the streets (ankle-high, knee-high, bridle of the horse's-high, mixed with corpses?). Because of the divergence of primary sources, chroniclers centuries after the event diverged, and sometimes with biases to fill (like William of Tyre). Even scholars today are trying to understand this, so Kedar set out to describe every single account of the massacre from then until the early 2000s. It's an interesting read...let me know if you wanna read it and I'll link it.