From 1646 till Manuel 11 was deposed in 1910 no Portuguese monarch has ever worn a crown. And the reason is this. In 1646 King João 1V, before the entire court at Vila Viçosa, took the crown from his own head and placed it at the feet of a statue of the Blessed Virgin and declared that she was to be the Queen and Patroness of Portugal under the title of the Immaculate Conception.
Then, by oath, he bound himself and his successors to defend the dogma that the Blessed Virgin was conceived free from original sin. The event was inscribed on stone tablets in every town in the land and Portugal became A Terra de Nossa Senhora.