The flag was instituted in November 1910, shortly after the establishment of the Republic in Portugal (October 5, 1910).

Green: green symbolizes hope for the future.

Red: the Red symbolizes the struggle of the people for the great ideals of equality, fraternity and Freedom and the sacrifices of the Portuguese people throughout its history.

Armillary sphere: Emblem of King Manuel I (1469 -1521). Symbolizes the Universe and the Portuguese discoveries.

The coat of arms, the castles, the corners evoke conquests, victories and legends (stories) connected to the foundation of Portugal by the king  Afonso Henriques (1109-1185).