
The origin of the word "Mariachi", according to tradition, is from the French language and goes back to 1862 when France invaded Mexico. The story claims that some French soldiers witnessed a Mexican rural wedding in which there was a group playing songs. One of the soldiers asked the translator "What is it?" and the translator responded "ç´est un mariage". And so the word "mariage" became popular and eventually evolved into the word "mariachi". However, there's also some people that claim the word originates from a similiar one in Otomí, a popular fact repeated in a song from the late Mexican legendary artist, Juan Gabriel, called "El Principio".
Originally the mariachis wore traditional rural costumes from Jalisco which consisted of cotton blankets and straw or palm leaf sombreros but later they took on the "charro" (cowboy/horse rider) look. The formal "charro" costume is made up of a short jacket and high tight black pants but the mariachi bands have also incorporated a white variation of the suit.
Most likely the "charro" costumes originate from the Spanish city of Salamanca, whose inhabitants are also called "charros". In the province of Salamanca between the Tormes river and Ciudad Rodrigo is a region called Campo Charro in which the typical cowboy suit was black with a short suit jacket and riding boots. The sombreros used, although very similar to the Mexican ones, had much smaller brims.

Nowadays you can find mariachi bands in many countries outside of Mexico such as Venezuela, where they are quite famous. In the United States, hundreds of bands have formed given the large number of Mexican immigrants who live there. You can also find them in Spain, playing in various cities, and singing traditional Mexican and Spanish songs while animating the streets of the city.
So there you have it folks, some insight into one of the most iconic symbols of Mexican culture.