Franco, who ruled Spain from 1939 to 1975 when he died, is buried in a valley just outside Madrid in an imposing basilica carved into a mountain-face with a 150-metre (490-feet) cross towering over it.
Known as the Valle de los Caidos (Valley of the Fallen), it is a deeply divisive symbol of a past that Spain still finds difficult to digest.
By late morning, a long line had built up of people waiting to attend a mass inside the vast structure after a far-right group called for a "national, patriotic and religious pilgrimage" to prevent "the plunder" of his grave by Spain's new Socialist government.
READ MORE: What you need to know about Spain's new government's vow to exhume Franco
As they gathered, demonstrators sang "Cara al Sol" -- the anthem of the fascist Phalange party, whose founder Jose Antonio Primo de Rivera is also buried at this divisive monument to the civil war and the dictatorship that followed.
Others were carrying flags of Spain under Franco, which were confiscated by the Guardia Civil police under a law banning acts exalting the civil war at the site.
Many on the left are repulsed by the site's existence, comparing it to a monument glorifying Hitler.
Under Prime Minister Pedro Sanchez, who took office on June 2, the new Socialist government has quickly pushed forward plans to exhume his remains, saying Spain "can't allow symbols that divide".
Instead, Madrid wants the site to be transformed into a "memorial to the victims of fascism".
But Franco's descendants are completely opposed to removing his remains, although no date has been set for the move.
The site also includes a crypt where the remains of some 27,000 fighters loyal to Franco are buried, as well as the bodies of 10,000 Republicans -- uniting in death those who once fought each other so bitterly during the civil war.
READ ALSO: Spain plans truth commission on civil war and Franco's dictatorship