The national flag of the Portuguese Republic, often referred to as the Portuguese flag, consists of a rectangular bicolour with a field divided into green on the hoist, and red on the fly. The version without laurels of the country’s national coat of arms stands in the middle of the Portuguese armillary sphere and shield, centered over the colour boundary at equal distance. The flag was announced in 1910, following the 5 October 1910 revolution, inspired by the colours of the Republican Party and the design of radical conspiratorial society the Carbonária.

The sphere and shield in the middle of the current flag are an integral part of the design, which has historically been centred on the royal arms, usually over fields of blue and white. Since the country's foundation, the standard developed from the blue cross-on-white armorial square banner of King Afonso I, through progressively more complex designs, which did incorporate green and red, 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