Catalan separatist leader Carles Puigdemont addressed more tens of thousands of supporters in Perpignan, a French city close to the Spanish border.
It's the first time the former president of the government in Catalonia had ventured so close to Spain since he fled to Brussels to escape prosecution.
Spain wants to put him on trial for sedition, as they have done with nine other separatist leaders who are serving long jail terms.
The regional prefecture said that 100,000 people attended the events though organisers said it was about 150,000.
Puigdemont played a role in organising the failed 2017 independence referendum in Catalonia, which sparked Spain's worst political crisis in decades.
"We must prepare for the final fight, overcoming errors, doubts, and weaknesses," Puigdemont said at the event.
Until now, Puigdemont had not risked travelling to France, which has close police and judicial collaboration with Madrid. But that changed recently when he was granted immunity as a member of the European parliament.