Inés Arrimadas of the Citizens Party in Catalonia told reporters before the march began that "the silent majority of Catalans are once again taking to the street to show that the majority of Catalans feel Catalan, Spanish and European".
Arrimadas walked out of the Catalan regional parliament on Saturday as it cast the vote for independence.
Frustrated by a defiant but divided Catalan Parliament, the central Government on Sunday began to assert control over Catalonia, firing the region's president, ministers, diplomats and police chiefs and transferring all authority to Madrid.
Since then, the secessionist leaders have been mostly absent from the public stage - not exactly in hiding, but close.
Puigdemont issued a brief prerecorded call for citizens to mount "a democratic opposition" to the takeover. No one was exactly sure what he meant.
Today the Belgian Migration Minister offered him political asylum - if Puigdemont needs it.
Two top leaders of the Catalan secessionist movement are already in jail, without bail, as prosecutors mull sedition charges.
El Periódico reported that Spain's Interior Ministry ordered the Catalan regional police stations to take down their portraits of Puigdemont.
The next showdown is scheduled for tomorrow when bureaucrats return to work and the doors open to the Catalan Government and Parliament.
Will Puigdemeont and his ministers return to work - or try to run a parallel government?
Oriol Junqueras, the Catalan vice-president dismissed by the Government of Spain's Prime Minister, Mariano Rajoy, warned in a regional publication that in coming days the independence movement "will have to make difficult decisions that will not always be easy to understand".
After being awarded sweeping powers by the Spanish Senate last week, the central Government published lists of more than 140 Catalan officials, alongside their advisers, who were being fired.
The Catalan Parliament was also dissolved by order of Spain, and new elections were scheduled for December 21.
Reuters quoted Íñigo Méndez de Vigo, a government spokesman in Madrid, saying, "If Puigdemont takes part in these elections, he can exercise this democratic opposition."
Today, the streets in Barelona belonged to pro-unity, pro-Spain voices.
Javier Rodriguez, 55, a banker said: "This is a big day, a day for the real Spain.They told us we weren't Spain. We are, today and always".
Asked what he thought of a declaration of a Catalan republic, he shook his head no. "This was a big fake. This republic is over, it is definitely over."
As he spoke helicopters circled over the demonstrators, each with the markings of a different force - the National Police, the Guardia Civil and regional Catalan police, d'Esquadra.
Manuel Garcia, 64, who served in Spain's Foreign Legion and as manger of the locker rooms of Barcelona's RCD Espanyol soccer team, said, "We came out to support the Spanish Government against this secessionist coup. What should happen to Puigdemont? All of them should be in jail."
