Cal Xertons stories and the forgotten histories (Cal Xertons pennas a i iar gobennas)

This is a set of large tomes, written full in the Elvish language. It tells stories of numerous historical sites, many unknown to the modern world.
The set of tomes feature five volumes, the first four fully written. The last tome seems to be written halfway full, before a large set of empty pages begin. The last, unfinished, chapter features the title "The isolated and forgotten city of Dirgarum".
The story present tells the tale of the thriving growing metropolis of Dirgarum. Which while still active with some local communities above ground, suddenly, seemingly overnight, disappeared. Not a single soul since has been seen.
The next page is empty, before the next writing is a lot less proper than the text before. "An ancient power under the name of Deveral Saldean now controls Dirgarum and named it Meghkohldur. Waiting for Takhisiss return so that he may take the surface again at her side. It is yet unknown who this Deveral person is, or was. It seems yet another corner of forgotten history."
The last page of this tome is written in a similar handwriting, featuring the following text: "To Remton and <corner of page ripped off>, if you may ever read this, these books were made for you. They contain our tellings of the forgotten histories of the plane, the results of our decades of travelling and storytelling.
It was our goal to give our children and theirs something to read that might inspire them. Things that happened way out here in the great world outside of Ulagon. It deeply saddens us that we failed to bring all of you that which we worked on for so long.
In case one of you finds our legacy, have grand adventures, and know that we shall always be with you. Eternal love, Kiaran and Velmar Cal Xerton."