Separatists declared victory in Thursday's regional election.
Earlier, Catalan leaders had said they would not accept Spanish authority.
It's one of the biggest pro-unity rallies amid Catalonia's independence crisis.
The government voted to strip Catalonia of its autonomy less than an hour after the region declared independence.
Catalonia declared independence on Friday. Minutes later, Spain imposed direct rule.
Spain is already fighting back.
The Spanish government has vowed to "sack" Puigdemont and his government amid rising tensions.
Mariano Rajoy said his government had taken this unprecedented decision to restore the law.
If Spain's prime minister invokes Article 155 of the 1978 constitution, it would not be fully effective until at least early next week.
President Carles Puigdemont requested more time for negotiations.
The region is divided over a movement to breakaway from Spain.
BARCELONA/MADRID, Oct 4 (Reuters) - Catalonia will move on Monday to declare independence from Spain following Oct. 1′s banned