Thousands of people, headed by King Felipe, came together to express their grief on Friday following the terror attacks in Barcelona on Thursday evening and Cambrils in their early hours of Friday morning.
The crowds paid tribute to the victims with a minute's silence followed by two minutes of applause and cries of "No tinc por" - "I'm not afraid" in Catalan.
The number of dead increased to 14 on Friday after a woman who was injured in the Cambrils attack died in hospital. Thirteen were killed when a van mowed down pedestrians in Barcelona's Las Ramblas on Thursday evening and more than 100 injured, 17 of them seriously.
The demonstration in the Plaza de Catalunya in Barcelona was also attended by Spain's prime minister Mariano Rajoy, deputy prime minister, Soraya Sáenz de Santamaría, and leaders of the country's main political parties, such as Pedro Sánchez (PSOE), Pablo Iglesias (Podemos) and Albert Rivera (Ciudadanos).
They stood alongside the president of the Catalonian government, Carles Puigdemont, his ministers and the mayor of Barcelona, Ada Colau.
Among the crowds were representatives of different religions, among them numerous muslims, joining in the general rejection of the attack.
Similar gatherings took place in Madrid and throughout Spain. A minute's silence was held outside Malaga city hall as well as at other town halls along the Costa del Sol.
On Friday morning police were still searching for the main suspect, Moussa Oukabir Soprano.