Graffiti - these marks, drawings or simple signatures that have traveled the walls of our historic monuments for centuries - intrigue and fascinate, but have only recently become the object of a heritage interest, beyond the curiosity they have always aroused. They form a heterogeneous group, addressing religion, love, sex, war, politics... Through twenty texts of researchers, anthropologists, historians or sociologists gathered for the first time, and through interviews with artists, the book questions their definitions and their multiple meanings. Testimonies of a period, echo of an event, description of the daily life of the prisoners or expression of a resistance, a political commitment, even artistic works: the graffiti can take on all these different roles. This book, abundantly illustrated, allows to embrace their multiple facets, become in our contemporary look traces, ultimate witnesses of a moment gone.