The Flag of Portugal (Portuguese: Bandeira de Portugal) is the national flag of the Portuguese Republic.
The Flag of Portugal is a rectangular bicolour with a field unevenly divided into green on the hoist, and red on the fly. The lesser version of the national coat of arms (i.e. armillary sphere and Portuguese shield) is centred over the colour boundary at equal distance from the upper and lower edges. On June 30, 1911, less than a year after the downfall of the constitutional monarchy, this design was officially adopted for the new national flag, after selection by a special commission whose members included Columbano Bordalo Pinheiro, João Chagas and Abel Botelho.
The conjugation of the new field colours, especially the use of green, was not traditional in the Portuguese national flag’s composition and represented a radical republican-inspired change that broke the bond with the former religious monarchical flag. Since a failed republican insurrection on January 31, 1891, red and green had been established as the colours of the Portuguese Republican Party and its associated movements, whose political prominence kept growing until it reached a culmination period following the Republican revolution of October 5, 1910. In the ensuing decades, these colours were popularly propagandized as representing the hope of the nation (green) and the blood (red) of those who died defending it, as a means to endow them with a more patriotic and dignified, therefore less political, sentiment.
The current Portuguese flag design represents a dramatic change in the evolution of the Portuguese standard, which had always been closely associated with the royal arms. Since the country’s foundation, the national flag developed from the blue cross-on-white armorial square banner of King Afonso I to the liberal monarchy’s arms over a blue-and-white rectangle. In between, major changes associated with determinant political events contributed to its evolution into the current design. Wikipedia