On September 16th, 1810, Father Hidalgo started the Revolution that was to lead to Mexico's independence from Spain. He rang the church bells and called on the people to take up arms.
On the night of the 15th, the President comes out on the balcony of the National Palace and rings the same bell that Father Hidalgo rang in his church in Dolores. Then the President repeats some of Hidalgo's words, starting with: "Mexicans, Long Live Mexico!" (¡Mexicanos, que Viva México!).
Flag vendors are everywhere, the plaza, walking the streets and in front of Sorianas. Independence day is the 16th but at midnight of the 15th 'El Grito' will be given from the second floor of the Melaque municipio building facing the plaza.
Both days the stores are not allowed to sell liquor so you'd better stock up for any home celebrations or just go out.
Ok, so my warning about liquor sales was totally wrong as there was open liquor sales both days. I've since heard that even election day there is no restricted sales. Now if I can remember who told me the first tale ???