The Alteran history book was the only text found among the treasures in Merlin's vault in Avalon. While reading it, Daniel Jackson learned about a race named the Alterans, who came to the Milky Way from another galaxy and built many "Astria Porta". Daniel immediately realized that the Alterans were the Ancients, and that they had evolved in another galaxy. What the book left out was why the Alterans left their galaxy — they were fleeing the Ori. (SG1: "Avalon, Part 2")