Several Millennia’s ago:
One day in the extremely distant past, an ancient convergence of leytones (sounds coming from leylines) from 2 converging leylines created life.
Life evolved throughout the eons and ultimately produced humanity. Humans found these convergences of leylines and built many of their early civilizations near or around them.
The convergences of leylines were treated as holy sites by early religions and the "mages" were religious leaders who studied the convergences and learned the first spells by directly copying the leyspeaking of the convergences of Leylines.
From there it's a matter of sharing or stealing the spells of other convergences which took quite a while.
Eventually someone began collecting them formally and learned that there are similarities in the spells that 2 leytones from 2 different leylines created when converging. They started making connections between the shared elements and the positions of the convergences of the leylines.
The theory of leylines was born and the leytones grew from that.
As one might imagine this isn't something that came together in a decade or even a century. This took millennia. A slow and laborious process plagued with many setbacks. Learning magic was a very slow burn and took a very long time.
For @The CodeXian Thinker @Leona The 7th @DjalliLind @K5S142 @The Mystic Chronomancer @TheNerdEternal1 @Can Perk @N0nartsy @Color Fixer Argalia @XavtheB @Non-Magical Girl, Island @Jacquese Walker @Urisbrak @Realhhhk6 @MaikoLen @Agent Facultas @Hestarne Hum. @Mr. Saggo Ramer @Omni-Absolute Jon and whoever else.