The monitoring of how public opinion memorizes the terrorist attacks from 13th November 2015, and moreover the terrorist attacks since the early 2000s, provides new material for understanding the evolution over time and the mechanisms of the construction of collective memory. Data collected to date show that these attacks had a greater impact on the population than other tragic events that have occurred in recent history in France, or even a greater impact than other and much more recent attacks. In the long term, the precise memory of the factual aspects and the memories of the personal circumstances in which people learned about the events begin to vanish. While imprecision is gaining ground, collective memory now crystallizes on very significant and overdetermined markers such as emblematic places or locations such as the "Bataclan". As a matter of fact, this imprecision of memory goes hand-in-hand with a much stronger symbolic and emotional investment of the event as a whole and leads to an overestimation of the number of terrorists or victims. The special place given to the terrorist attacks of 13th November in the collective memory is due to the unprecedented number of victims, the fact that the attacks took place in the heart of the capital city, the reaction of the public authorities who declared a long lasting state of emergency, the discursive framing of the war on terrorism in all major media, and the feeling that the Islamist threat can kill indiscriminately without targeting specific categories of the population. The study also reveals the influence of value systems (political opinions, views of the republican model) and social characteristics of individuals on the way people memorize such experiences. It is part of a fundamentally multidisciplinary research around "Memory and trauma" that includes neuroscience, biological and clinical investigations.