There are ten classes of magic. Class ten is the highest category. Any vampire can achieve to do magic until class 2 through effort, but from class 3 on, things are determined by talent. Nergal is the only class 10 magician in Crepuscule. Magic isn't widespread yet in Crepuscule and the world restricts the places where one can learn it. Arzew is one of the places where a vampire can learn magic.
Magic often results to the appearance of a magic circle. Also, magic ceremonies, some or all of them, require first the drawing of a magic circle.
This was later revealed to be due to the contract made by the vampires stating that only vampires could have magical powers and the contract would take away magic from the humans meaning future humans would be born with no mana therefore they could not be able to do magic, However there is an exception Lark a Crimson Eyed Human was born with an infinite amount of mana.
This was later revealed to be due to a rare few humans managed to break the contract and keep there magic, there descendents being the Crimson Eyed Humans. Humans born with magic, red being the symbol for magic.