The Senyera[a] is a vexillological symbol based on the coat of arms of the Crown of Aragon, which consists of four red stripes on a yellow field.

Furthermore, the Pennon of the Conquest of Valencia is documented as the world's oldest extant flag, dating from 1238, even though the yellow part was originally white, but the red stripes design was the same.

It is thus present in the flags and shields of the territories that once were part of the Crown of Aragon and also in the arms of Andorra, Provence-Côte d'Azur and Sicily among others.

According to the Encyclopædia Britannica, the flag of the Holy See's Navy from the 12th century on consisted of two vertical red and yellow bands, sometimes bearing the tiara and the keys.

According to the Vatican official website, the yellow and red of the flag of the Holy See were two colours traditional of the Roman Senate and People.

This author reports that Pope Innocent III after crowning the King Pedro II (the Catholic) accepted that Aragon was a tributary kingdom of the Apostolic See.

According to a 14th-century legend, the flag dates back from the 9th century, when the four red bars were drawn, as an act of gratitude, on Wilfred I the Hairy's (Count of Barcelona) golden shield by king Charles the Bald's fingers drenched with blood from the Count's war wounds prior to Wilfred's death in 897 during the siege of Barcelona by Lobo ibn Mohammed, the Moorish governor of Lleida.

Romantic-driven Catalan nationalists were particularly keen on this legend during the Renaixença, in the 19th century, albeit it has always been recognized and divulged as such even in patriotic circles.

For instance, in Aragon an extra coat-of-arms, in Balearic Islands a castle in the canton, and in València a blue crowned fringe on the hoist.