The following is a short article wrote a few years ago:
Some poorly informed sources may translate El Grito de Dolores as the scream of pain (dont laugh, I saw it written so in the English section of a Cozumel newspaper once!), but it actually means the The Cry of Dolores and refers to the cry for independence made by the catholic priest Miguel Gregorio Antonio Ignacio Hidalgo y Costilla Gallaga Mandarte Villaseñor (a.k.a. Miguel Hidalgo) in the town of Dolores, Mexico in the early morning of September 16, 1810 (and not September 15, as popularly believed).
Hidalgo was involved in a planned revolt against the Spanish rulers of Mexico, but word of the plan reached the authorities and when he got wind of his impending arrest, he preempted the authorities and ordered his brother to take a contingent of armed rebels and free the political prisoners being held in the city jail on the night of September 15, 1810. Early the next morning, Hidalgo ordered the church bells to be rung while he, Ignacio Allende, and Juan Aldama went out in front of the church and urged the townsfolk to revolt. Four days later, the Battle of Guanajuato (a town just south of Dolores) occurred and the Mexican War of Independence was begun. It would not be until September 27, 1821, however, that Mexico was actually free of Spains domination.
The words uttered by Hidalgo at the end of his speech on that fateful day were not recorded by anyone present at the time, but many different versions have been passed down as the true ending. Samples of a few of the purported exact quotes (translated into English) are:
"Long live religion! Long live America! Down with bad government!
Long live America! Down with bad government! Long live our Holy Mother of Guadalupe!
"Long live Our Lady of Guadalupe! Death to bad government! Death to the Spaniards!"
Long live Our Lady of Guadalupe! Death to bad government! Death to the gachupines!
The now familiar shout of Viva Mexico! at the end of the Grito was not a part of Hidalgo's original speech, nor was the recital of the Mexican revolutionaries names; all that was added much later. The reenactment of the Grito de Dolores has become an integral part of the Mexican peoples celebration of their Independence Day, but over the years it has morphed with the addition of new patriotic lines and the deletion of others.
The day the Grito is uttered has also been modified; up until 1910, the cry was made on September 16. Mexican President Porfirio Díaz, however, mandated that the Grito be moved up to September 15, to coincide with his birthday. This new, flexible, version of the Grito is shouted by the President of Mexico every year on September 15, at 11 PM from the balcony of the National Palace in front of the Zócalo (the Plaza Mayor) in Mexico City as the bell of the palace rings. At the same time, all across the country, a similar but locally-customized patriotic cry is offered up by the Mexican state governors and Mexican city mayors.