A human chain made of 175,000 people stretched 200 kilometers (124 miles) Sunday in a display to demand an independence vote for the Basque region in northern Spain.
The Basque Country enjoys higher levels of self-determination than any of Spain's other sixteen regions, with its own police force, education system, language and special financial arrangement with Madrid.
Several pro-independence political groups and unions backed the initiative and figures from the local ruling Basque National Party joined the event.
The Spanish Constitution, created in 1978 following the end of General Francisco Franco's dictatorship, states that the country is indivisible, referring to the "indissoluble unity of the Spanish Nation".
The chain wasn't strictly about the right to vote for independence.
Former Prime Minister Mariano Rajoy, who was widely criticised for his handling of the Catalan crisis, was ousted from office in a no-confidence vote on June 1.
Sanchez, who now heads the government following the vote, has called for renewed talks with the Catalan leadership.
Last year, a banned referendum on Catalonia's separation from Spain and consequent unilateral declaration of independence by the regional government prompted Madrid to impose direct rule over the region.