In January 1967 a fire destroyed the Altar del Perdón and almost all the choir stalls of the Mexico City cathedral.  The following months  and years witnessed a political, artistic, and religious debate on the best way to restore the cathedral's nave. Two factions arose almost at once, openly  and harshly  opposed.  On  the one hand,  the Neo-Baroque party, led by the historians Edmundo O'Gorman and Francisco de la Maza, who ordered  the civil and church authorities to restore the nave just as it had been before the fire. On the other hand, the Modernist party, led by the architects Mario Pani and Ricardo de Robina, who proposed a new emplacement for the altar and chancel, in order to adapt the cathedral's interior to the liturgical instructions dictated  by the II Vatican Council.  This work analyzes both parties' arguments and reflects on their relevance for the history of contemporary ideas in Mexico.