On November 17, 2005; the Brazilian State of Piauí modified the flag. On that date the State Law 5.507 proclaimed:
"Article 1st. The Flag of the State of Piauí, defined by the Law 1050 of June 24, 1922, will contain the date of *13 de Março de 1823* (March 13,1823) the day of the Battle of Jenipapo, written in white, capital letters, in the blue rectangle above the star"
This date, March 13, 1823, is the day of the Batalha do Jenipapo (Battle of Genipap) the bloody battle in the Independence war of Brazil. At the banks of the Jenipapo river where today is located the city of Campo Maior-Piauí the Brazilians patriots fight fought against Portuguese troops, and the date is considered the date of the entry of Piauí into the Independent Brazilian Empire. The province of Piauí has a strategic position for the maintenance of the North of Portuguese America between Amazonia and the Northeastern provinces, this is the reason why Portugal appointed the Governor-in-army of the Province the veteran of Napoleonic Wars João José da Cunha Fidié.
In Piauí the first city to claim its adhesion to the Empire was Parnaíba in the extreme north of the State, this initiative was the reason for the relocation of Portuguese troops from Oeiras (the capital of the province at that time) to Parnaíba, these troops commanded by Major Fidié, when the Portuguese troops were in Parnaíba in January of 1823,the cities of Piracuruca, Matões e Oeiras, also claimed entry to the Empire and in February of 1823 was the time of the city of Campo Maior claim the same entry. In March of 1823 the troops left Parnaíba to try to subdue those cities, and at the banks of the River Jenipapo the big combat happened, a great part of the local population fought against the Portuguese troops, the Portuguese troops having superiority of arms, soldiers and training. In March 13, 1823, after five wars of battle under a boiling hot sun, the Piauians 700 casualities and the Portuguese around 100. Portugal won this battle, but this battle was a the first of the war in Piauí and in April of 1823 the troops of the Major Fidié was obliged to retreat to Maranhão, a province loyal to the Portuguese Crown, but in June of 1824 after the Battle of Caxias the troops of Ceará and Piauí, supported by the patriots of Maranhão defeated the troops of the Major Fidié, consolidating the independence of these provinces and the entry of these provinces in the Empire.