Founding moments of nations seem intrinsically significant. Nevertheless commemorations of the Bicentennial of Mexico Independence and the Centennial of Mexican Revolution will show that the meanings of such events are constructed on the basis of contemporary politics. The article analizes which dimensions of that political past are malleable (and to what extent) and which are relatively fixed (as inserted in myths, but also in institutional legacies).El articulo analiza la manera en que las conmemoraciones del Bicentenario de la Independencia y el Centenario de la Revolucion Mexicana reconstruyen o redefinen significados historicamente sedimentados, en funcion de la politica presente. ¿Que dimensiones de ese pasado politico se revelan como absolutamente "maleables" y cuales parecen estar relativamente fijadas (por su insercion en mitos politicos pero tambien en herencias institucionales)?