Hernán Pérez de Oliva wrote a history of conquest of Mexico using a specific source: the “Second Letter” of Hernán Cortés. In his text Pérez de Oliva introduced some formal changes that reveal his ideological opinions, a point of view very different from the position of his source. Two of the rhetorical ways to produce those changes are brevitas and amplificatio. That ideological difference shows us the Pérez de Oliva’s humanist perspective about the landmark event of the conquest of the Nueva España.