"Unity" is the central theme as officials and Spaniards mark their national holiday on Thursday with parades, rallies and memorials.
The holiday comes as Spain navigates one of its worst political crises since the country's return to democracy four decades ago. On Wednesday, Spain's central government gave Catalonia one week to clarify if it will push ahead with declaring independence.
Pro-unity supporters tied Spanish flags to windows and balconies around Madrid where Prime Minister Mariano Rajoy and King Felepe VI attended a traditional military parade.
Around 3,900 troops from Spain's armed forces took part in a procession along Madrid's Paseo de la Castellana boulevard.
In the Catalan capital, Barcelona, a pro-unity rally organized by the far-right is expected to take place.
The holiday, which marks the day that Christopher Columbus first arrived in the Americas in 1492, will also pay tribute to the victims of a recent terror attack in Barcelona.
The 16 victims will be represented by ambassadors from their countries of origin — Argentina, Belgium, Canada, United States, Germany, Italy, Portugal, United Kingdom and Australia.
Tensions are running high in Spain after the wealthy, northeastern region of Catalonia voted for independence in a banned referendum on October 1.
Rajoy said on Wednesday that the central government gave Catalonia's President Carles Puigdemont until Monday to clarify whether the region had declared independence from Spain.
In the event the Catalan president declared independence, he would have until next Thursday to rescind it, otherwise Madrid would suspend Catalonia's regional autonomy, Rajoy added.
His warning came after Puigdemont announced on Tuesday that he was proceeding with a declaration of independence, but was suspending its implementation to allow for talks with Madrid.
Catalonia's bid for independence has raised concerns about the stability of the European Union with Brussels urging "full respect of the Spanish constitutional order."
German Foreign Minister Sigmar Gabriel said that a unilateral independence declaration would be "irresponsible," while France said it would not recognize Catalonia's bid for statehood.
rs/kms (AFP, EFE)