The Binding of Magic.

Nearly four thousand years ago, the Elder Ones formed an order called Lore Keepers of the Arcanum.  The Lore Keepers traveled around the known world and beyond, it's even said they went to the Far Place, looking for lost secrets and ancient, magical texts.  In those days, magic flowed through the lands like water, uncontrolled, and wild.  The Keepers decided to do the impossible, bind magic to understandable laws, they prayed to their Gods for guidance, and meditated on it for many nights, they finally decided to do it.  They went on top of Mt. Asvederus*, there they drew an enormous sigil in the ground and wrote Magic's true name, the Keepers then cast a long, powerful, mana-sapping, ritual, that bound Magic to their laws.  After the Binding ritual, the gathered mages wrote down the more powerful secrets they had found, the way to do the Binding ritual, the magic laws, and the true name of Magic, but Sealed the back part withe true name in it, in a vast book called the Codex Arcana.  The Lore Keepers of the Arcanum have survived through the centuries, though they have gotten slightly smaller, the Binding Sigil is now watched over by the White Mages.  And the Codex Arcana was taken to a mysterious island called Dragongard.

*Asvederus was a tenth century alvurean priest-king, read more in the Royal Documentation of Alvurean History.