Before the founding of Equestria, the only one of the three tribes to display any formal military capacity was the pegasus tribe. Their architecture is reminiscent of ancient Greeks, and armour and weapons reminiscent of hoplite soldiers (such as plumed helmet and doru [spears]).
The modern day-Equestria Royal Guards sport armour more along the Roman pattern, with Imperial-style galea and neck guards. Unlike their predeccesors, the Royal Guards membership is not exclusive to pegasi.
These have been seen accompanying Celestia outside Canterlot, due to their wings allowing them to keep up with her. They are often seen pulling the royal chariot to transport her, though they have also been seen flying in formation with the princess. They all sport white coats and golden armor, with blue tails and plumes on their helmets. They have a speaking role in A Bird In The Hoof, both speaking in gruff, masculine voices and scowling through most of the episode. They also take inspiration from the British Royal Guards, in that they are totally still and silent until someone tries to pass without authorization.
Luna's Pegasus GuardThe guards who serve Princess Luna are far more menacing and intimidating in their appearance, having bat-like wings, dark coats as well as purple armor. Their armour seems very elaborate and similar to the unicorn guard bellow, this might therefore be dress armour specifically made for the Nightmare Night festival.
Unicorn GuardThese guards sport grey coats, silver plumes and tails. They guard Celestia within Canterlot. Unlike the Pegasus Guard, they have mostly served as background ponies. These guards are seen around Celestia's throne in the
opening theme of the show and in The Cutie Mark Chronicles during the summer sun celebration. A single guard was seen in Sweet and Elite, guarding the entrance to the VIP box for the Wonderbolts derby. When Rarity attempted to enter, the guard stopped for and inspected
her but allowed her to enter when Fancy Pants recognized her as his guest.
Fan ReactionTheir clone trooper-alike visual similarity has raised some amusement among the fandom, though most accept the simple explanation that they dye their coats and tails to serve as a uniform.
Their visual and vocal similarity with the game Oblivion's famously hammy guards has also led to much amusement.