Paq'batlh is a holy series of Klingon scrolls, also known as the Book of Honor, which details the history and stories of Kahless the Unforgettable. The sides of the scrolls consist of imagery of d'k tahgs, bat'leths and the emblem of the Klingon Empire.
Among the scrolls in the Paq'batlh are the Tomes of Klavek which tell the story of how Kahless returned from the underworld of Gre'thor with a scar after redeeming the honor of his brother Morath. The tomes say that Kahless kept the scar from his journey as a reminder and as proof of how real his descent to the underworld was. (VOY episode: "Barge of the Dead")