National audienceThis article observes a cultural interaction process by considering the way in which the cattle imported from Europe, particularly the bull, got to merge into the indigenous mythical world. The author presents two opposite worlds in the XVIth century : the « lords of herds » and the indigenous communities from the valley of Toluca (Mexican Central Highlands). In the XVIIth century, the young Indian Republics adopt a figure that comes from the European imaginary, the Siren, symbol of the « lords of the water », lords of the dead in the Otomi cosmogony. The contemporary rituals of rain petition associate the genesic strength of the bull to the indigenous cosmogony : absorbed in the world of the civilizing heroes, the bull act...