The march came just two days before Mr Puigdemont is expected to make a key address to the Catalan parliament, which opposition sources have reportedly claimed will see him make a unilateral declaration of independence.
Some 90% of Catalans who voted in a disputed referendum on Oct.1 backed independence.
Mario Vargas Llosa, the Peruvian-born author known for his right-wing views, is attending the rally and has denounced Catalan independence, calling it a nationalist movement that will bring down Spain. As for Spain's hard-left Podemos party, its leader Pablo Iglesias was roundly booed by some 50 pro-unity demonstrators when he was spotted at Barcelona Sants railway station early yesterday morning - catching a train for Madrid.
"We believe that we know what the Spanish people are thinking". "This crisis needs to be resolved through dialogue at all levels of Spanish politics", France's European affairs minister Nathalie Loiseau said.
If it became independent, Catalonia would automatically be excluded from the european Union, it could join only after a new accession process.
Instead, Catalan president Carles Puigdemont would make a "symbolic statement" and speak of embarking on a path leading towards independence.
Florida Hospital collects donations for Puerto Rico relief efforts
In addition, two New Jersey National Guard armories continue to accept donations to aid Puerto Rico hurricane relief efforts. Cruz said, "This is what being a police officer is all about, and this is why we're going down there.
Catalonia's Parliament had been due to meet on Monday with the expectation that it would endorse the declaration of independence.
He also says that moves by banks and multinationals during the past week to relocate their base outside of Catalonia because of the political uncertainty are "absolutely shameful" and a "blackmail to the decision of the Catalan people".
France, on the other hand, said that they will not be recognizing Catalonia should it declare its independence on Tuesday.
"Given the negative implications of independence for economic activity in Catalonia due to its likely exclusion from the European Union and euro area, we think the likelihood of independence is very low", a note from JP Morgan analysts read today.
On the eve of Sunday's rally, Spain's Prime Minister Mariano Rajoy refused to rule out suspending Catalonia's regional autonomy - a move that risks further unrest. "We will apply what the law says", he told Catalonia's TV3.
Ever since Spain's return to democracy in the 1970s, Madrid has struggled to balance the country's patchwork of regional identities, including its decades-long fight to quell separatism in the northern Basque Country led by violent militants ETA. It is home to 7.5 million people and accounts for about a fifth of Spain's economy. Less than half the electorate of the region participated in the vote last Sunday.