"Originally called the Praetorian Guard, the Royal Guard were originally a royal defense force, however since the abolishment of the Equestrian Military after Princess Luna was banished, they have filled the niche as a Paramilitary, Guerilla, and now replacing the Original Equestrian Police Force in areas that haven't been annexed by the Aztecan Government" - Terminal Log #2 The Royal Guard is a major Faction in Equestrian Revelations
Armed, Dangerous (To Criminals, and most Mercenaries) and Quiet, can describe Royal Guard members on patrol, however unlike most Police Forces on Earth, they are not Corrupt or do they use violence against Innocents. When not Patrol, they working hard on solving cases, fixing problems, interrogating captured criminals and doing paper work or relaxing after a hard day at work.
Formed sometime after the Equestrian War of Indepence, the Royal Guard was originally named the Praetoriian Guard, and was originally formed as protectors of the Emperors/Empresses. When the Equestrian Military was abolished/dissolved in 351 CE, the Praetoriian Guard filled the niche left by them and specialized in Paramilitary, and Guerilla Local Warfare. They were renamed in 764, when they became more of a Military Police Force.
In 1239 the Equestrian Government signed The Royal Guard Re-Arnament Pact, with AzTech, who supplied materials and blueprints to a gun company who in turn would manufacture weapons for the Royal Guard, eventually by 1246 the Royal Guard absorbed all Police Forces (Other than Baltimare, Stalliongrad, Manehatten, Seaddle, San Ponygo, Las Pegas, Los Pegasus, and the Canterlot Royal Police Force who maintained their indepence) thus filling the Role entirely of a Military Police Force.
Due to Equestrian Laws, the Royal Guard is made exclusivly of Ponies, except for few exceptions. If a non pony wishes to join the Royal Guard, they become Mercenaries.
Recruit - Newly joined ponies, they are loud, and immature but a loyal force.
Standard - Standard Royal Guards.
Legionaires - Royal Guards that are trained solely for combat, mostly a Riot Squad, or Anti-Gang force.
Decanus - Commanders of 10 Troopers in a Legion.
Centurions - Highest Ranking Legionaires, they normally control groups of 100 troopers.
Velites - Light Riot Troopers, armed with Light Firearms, and Throwing Spears.
Rangers - Royal Guards that operate in Rural areas.
Vexillarius - Royal Guards that boost morale of other trooper, they have large banners, wear bear or wolf skins around their head, and are Guerilla Masters.
Wendigos - Royal Guards armed with advanced weapons and armor the Royal Guard pact can get them, only used as a last resort.
Praetorrians - Royal Guard Members that are solely for the pretection of Government Officials, Princes and the Princesses.
Commanders - High Ranking Members, rarely seen in forces, they however will Patrol by themselves if they are not doing important desk work. Shining Armor is an Example of one.
Legate - The Highest Ranking Member, they are two of them, one male, and one female, they do not go out on patrol.