"The RURALES, or Gendarmeria Fiscal "Rurales," or state police delegated to law enforcement in the countryside, had existed in Mexico since the 1840's. However, these country police were sort of re-founded as the "Gendarmeria Fiscal" in 1885 by the then president of Mexico Porifirio Diaz. He promoted it as an elite unit of military police controlled directly by the Ministry of Finance. However, in reality the Gendarmeria Fiscal answered only to President Diaz. It was the 'Great Dictator', and only he, who had the authority to appoint or promote officers of the gendarmeria. This was because he needed to insure the complete loyalty of an organization that also served as his unofficial secret police force. The gendarmeria provided him with very complete reports on just about everything and everyone in Mexico. Furthermore, under the guise of law enforcement, and with very little encouragement necessary from the president, the gendarmeria permanently disposed of troublesome dissidents. They appear to have been a really handy group for a dictator like Diaz to have around.
The gendarmeria's official job was to protect payrolls, chase Indians, catch smugglers, and defend banks along the national frontier. Or to quote from their foundation charter of 1885, "The exclusive purpose of the Rurale Police is to maintain security on the highways, assist the city police, protect the safety of all citizens, prevent transgressions of the law, pursue apprehend and place at the disposal of the authorities all criminals." Troopers served four year enlistments, were considered to be "perpetually on duty," and were to remain constantly armed. The minimum weaponry permitted was describe as "at least a saber." Their nickname 'Rurales' was later justified because they were always patrolling the countryside and never in garrison. A second nickname for the gendarmeria was the 'Cordada'. This title has never been fully explained, although it probably has something to do with the verb cordar to rope. Kosterlitzky was sometimes referred to as 'Juez de Cordada' (Judge of the roped ones). Suggestions that the name grew out of the rurales affinity for hanging suspects founders on their actual preference for the 'El ley de fugo' (shot while trying to escape). Much hearty laughter was enjoyed by the enlisted men over this practice at suspects' expense. The most common joke being, "He got away, but just a little away."
If the officers of the gendarmeria were a hand-picked elite the enlisted men were, well, they were the scum of the earth, as their previously described taste in humor might suggest. Official documents stressed the high standards required of al recruits, however, the theory amongst most civilians was that a conscious effort was made by all gendarmeria officers to recruit men of the most horrifying, abysmally low character possible. Kosterlitzky had a personal preference for convicted murderers. The plan seems to have been to form a nation wide organization along the lines of the 'Dirty Dozen'. New recruits were issued with a light grey undress uniform and a large grey sombrero unless, as the story goes, they had been serving a murder sentence in which case they were given a black sombrero. A quick scan through photos of the rurales on campaign reveals black hats showing up with what contemporaries called a terrifying frequency." Source ~ The Bengal Club.