The occupants of the city of Alidia

Alidians

They usually grow to be tall and long-limbed

Females usually have light pastel colors, and males are a little brighter

6-7 feet

N/A

Pureblooded Alicorns usually reach maturity before earning their Cutie Marks

Males have broader wings than females, as well as curved horns

Armor
Specially fitted to the particular Alicorn, and embedded with crystals from the trees beneath the city. These crystals act as amplifiers and greatly enhance the magical capabilities of the user.

Extreme magical prowess, vast intellect

Pride, vanity

Foals are either born as unicorns or pegasi. They must train to ascend to full alicorn status and receive what they lack. As such, whatever they were born with is their strongest appendage. Alicorns who were born as pegasi grow up as adept fliers, while those born with horns are stronger magic users.
Once in a blue moon, a full alicorn is born. These sacred individuals are destined to become The Crystal Keepers.

The Keeper Ceremony

The defeat of the many-legged monster, Silurian. For years Alidia was hunted by this creature, who had a taste for their flesh. Their magic could not pierce its thick armor, and their walls could not hold the enormous monster back.

Becoming an alicorn requires vast amounts of magic, in order to create the implement that is lacking. For Alidians this is an easier process compared to regular unicorns or pegasi, because they already possess large magic stores, so outside influence doesn't have to be super intense.