2014 In the 21st century, identities are multiple and changing. Therefore, seen from today, it is very surprising the intensity and persistence with which the Catalan identity has been maintained during the last three centuries. In this chapter of the "300" series we review how collective memory, a differentiated economy, the maintenance of one's own language and an unbeatable civil society have led this identity to the 21st century. After the War of the Spanish Succession, the victors built a great fortress in Barcelona, the Citadel. This fortress served to monitor the city and to suppress its protests, but it also became a permanent reminder of the defeat in the war and the lost constitutions. The Citadel, unwittingly, maintained the historical memory for several generations. And the people of Barcelona did not stop until it was demolished.