February 24th is El Día de la Bandera de México, commemorating the day in 1821 on which the Plan of the Three Guarantees — religion, independence, and unity — was proclaimed by Generals Agustin de Iturbide and Vincente Guerrero, and the first three-color flag for an independent Mexico was created by José Magdaleno Ocampo.

Flag Day has gotten a lot bigger, literally, with the construction of the Banderas Monumentales — monumental flags, flown on massive flagpoles, in various locations across the country.
A short documentary from NotimexTV on the construction of the giant flags by the Secretariat of National Defense.
Flag Day is a time to recite el Juramento a la Bandera (the Oath to the Flag)…
¡Bandera de México! / Flag of Mexico!
Legado de nuestros héroes, / Legacy of our heroes,
símbolo de la unidad / symbol of the unity
de nuestros padres y nuestros hermanos. /of our parents and our brothers.
Te prometemos ser siempre fieles / We promise to always be loyal
a los principios de libertad y de justicia / to the principles of liberty and justice
que hacen de nuestra patria la nación independiente, humana y generosa / that make our homeland the independent nation, humane and generous
a la que entregamos nuestra existencia. / to which we give our existence.
… and to sing el Toque de Bandera (the Salute to the Flag):
Se levanta en el mástil mi bandera / My flag rises on the mast
como un sol entre céfiros y trinos / like a sun between winds and warbles
muy adentro en el templo de mi veneración, /inside the very temple of my veneration
oigo y siento contento latir mi corazón / I hear and feel my heart beating happily
Es mi bandera, la enseña nacional, / it’s my flag, the national standard,
son estas notas su cántico marcial. / these notes are its martial canticle.
Desde niños sabremos venerarla / From childhood we’ll know how to venerate it
Y también por su amor, ¡vivir! / and also for its love, to live!
Almo y sacro pendón que en nuestro anhelo / Venerable and sacred banner of our yearning
como rayo de luz se eleva al cielo / like a ray of light rises to the sky
inundando a través de su lienzo tricolor / flooding through its three-colored canvas
inmortal nuestro ser de fervor y patrio ardor. / our immortal being of fervor and homeland ardor.
Es mi bandera, la enseña nacional, / It’s my flag, the national standard,
son estas notas su cántico marcial. / these notes are its martial canticle.
Desde niños sabremos venerarla / Since childhood we’ll know how to venerate it
Y también por su amor, ¡morir! / and also for its love, to die!
The Salute to the Flag, performed by the Genaro Nuñez Band and the Student Band of the State of Jalisco.
Here’s a handy infographic on the Mexican flag — for those who read Spanish.