At some point between the sinking of Atlantis (c.6586 B.C.) and when Solon first hears about the lost continent (c.640 B.C.), Aziz happened upon a deep schism in the earth. This would lead him to Atlantis, discovering it to be still thriving.
Over a two year period, Aziz learned about it's culture, language, and, most of all, the crystals that serve as their power source. As King Kashekim Nedakh would have had outsiders killed on sight to protect Atlantis, the shepherd would conduct his research as secretly and discreetly as possible. He would also presumably steal a crystal before leaving.
Upon returning to the surface, Aziz was declared a madman and sent to an asylum. While imprisoned, he would write on numerous scrolls about his discovery in great detail. This included directions on how to reach Atlantis and an understanding of the people and its culture. However, he would document all of this in the Atlantean Language and thus they would be immediately dismissed as incomprehensible scribbles.
In the centuries to come, his writings would be sought after by many cultures, societies, and individual figures. They would either look to it as a source of inspiration to improve upon their lives or to actually conduct an expedition to the fabled lost continent. These writings would originally be christened The Scrolls of Aziz, but it would later be known as The Shepherd's Journal.