Raphaëlle Branche’s book, L’Embuscade de Palestro, Algérie 1956, offers to give a more exact definition of the events that took place on 18th May 1956 in the Isser Valley, to question the transformation of the ambush into a massacre and to bring the event to light based on the study of the colonial past of the region since the end of the 1860s. Palestro is treated as an anthropological fact whose comprehension requires to take into account the participation of the local population, being itself the stake of the conflict opposing the French Army to the ALN. This violence - linked here to the memory of the 1971 insurrection in Kabylia which had already spurred a first cycle of violence and repression - is tackled from the viewpoint of its reception in France, whose share of colonial representations is brought to light by the author. But the very importance of Palestro demanded further analysis. The hypothesis according to which it recalls to collective memory the first colonisers’ massacres in 1871 are insufficiently developed. The historic approach remains incomplete and runs into the logical and methodological problem of causal inference as it seeks to recount the acting intentions of individuals from behavioural observation data.