This doctoral thesis intends to propose a commentary of the Chanson de Roland, based on a meticulous analysis of all the variants which have reached posterity. By paying close attention to the whole of French versions and by refusing to comment the sole manuscript of Oxford, as most of scholars do, we comply with the unsettled nature of medieval poetry and furthermore support the idea that the Chanson de Roland should be considered as a myth. The comparative mythology thus constitutes a main thrust of this work : in the tradition on Indo-european studies as founded by Georges Dumézil, we compare the myth of Roland to the myth of Balder, on a morphological level. The essay of comparative mythology is the first part of our commentary and could be regarded as self-reliant. However, it forms a single entity with the essay of typological comparison which follows. The thesis actually intends to interpret the poem in the light of the theory developed by René Girard, which allows to analyze the aesthetics and the ideology of the chanson de geste in a new light. The poetic of repetition and the art of symmetry are closely linked to the hypothesis of mimetic desire, just like the epic crisis is closely linked to the model of the sacrificial crisis. By studying the anthropological question of violence and the ambiguous figure of mythical warrior, this work combines two approaches, deemed to be irreconcilable and nevertheless complementary, in the sense that they interpret in the same way the ambivalence of epic heroes.