Thousands poured into the streets of Barcelona on Monday to show their anger after Spain's Supreme Court in Madrid jailed nine Catalan separatist leaders to between nine and 13 years each.
Clashes broke out in front of police headquarters in Barcelona, where riot police cracked down on separatists in an effort to disperse the ocean of demonstrators.
And - protesters blocked the highway to the El Prat Airport, with tensions bubbling over into the terminals.
Protesters vowed this was only the beginning.
(SOUNDBITE) (Spanish) BIO-MEDICINE RESEARCHER, ALBERT, 28, SAYING: "We are here protesting peacefully because of the unfair and disproportionate rulings.
This (protests) has just begun… we will continue to be like this until we achieve our goal which is independence." In Madrid, however, some welcomed the sentences.
(SOUNDBITE) (Spanish) MADRID RESIDENT, ANTONIA MINCACHAGUA, SAYING: "It is the correct sentence.
My humble position is that if they have to pay, they should pay for their guilt." The drive for independence in 2017 culminated in a banned referendum and a short-lived declaration of independence, that triggered Spain's biggest political crisis in decades, before Madrid stepped in to impose direct rule.
The nine Catalan leaders were jailed for sedition, while another three were convicted of disobedience and not given prison sentences.
All were cleared of the gravest charge: rebellion.
After its ruling, the Supreme Court issued a European arrest warrant for Carles Puigdemont - the former regional head of Catalonia who lives in self-imposed exile in Belgium.
He called the sentences an "atrocity" and said now was the time to react "like never before." Spain's government has said it's ready to take direct control of Catalonia once again if secessionist leaders there break the law.