|Abstract||Since 1968, the Tlatelolco Massacre has been called, by some, a dividing line in Mexican history. For intellectuals, it represents the fourth break in Mexican history. The first three breaks were the Conquest in 1521, the wars of independence beginning in 1810, and the Mexican Revolution of 1910. The Tlatelolco Massacre, then, has been seen as a nation-defining event. But intellectuals were not the only ones for whom Tlatelolco was important. The ruling Partido de la Revolucion Institucional (PRI) had a vested interest in forgetting the massacre. For the PRI, which saw itself as the Mexican Revolution's ideological guardian, the massacre was an unfortunate, but minor event. For the forty years considered in this study, the battle between the two groups has been over how to remember the massacre and how to fit it into the revolutionary narrative. Using memory studies, I examine how the massacre has been remembered and forgotten, and how memories have changed over time.^Pioneering studies by Maurice Halbwachs, regarding collective memory, and Pierre Nora, regarding how memory and history converge, have guided my analysis. Emily S. Rosenberg's A Date Which Will Live (2003) is another important influence for its discussion of how the Japanese attack on Pearl Harbor has been seen since 1941. Also important have been works by Tlatelolco veterans like Elena Poniatowska, Carlos Monsivais, Ramon Ramirez, Gilberto Guevara Niebla, and Raul Alvarez Garin, which illustrate the intellectual idea of the fourth break. While the concept of the fourth break is interesting, intellectuals never convince the broader Mexican public of its efficacy. Consequently, intellectuals withdrew from the leadership position they assumed after the massacre and stopped engaging the public. Instead, they published the same arguments time and again, but only for themselves. At the same time, Tlatelolco never fully disappeared from the public eye.^Jorge Fons reinforced the intellectual theory of the fourth break with his film Rojo amanecer (1990). Cuauhtemoc Cardenas declared a day of mourning on 2 October 1998, and Vicente Fox appointed Special Prosecutor Ignacio Carrillo Prieto to investigate not just Tlatelolco, but all the social movements from the 1940s to the 1970s. Thus, despite new information becoming more available, the intellectual pole refused to evolve and take it into consideration. As a result, Tlatelolco still exists in a netherworld.