Recently a reader posed one of those inherently fundamental questions that never occur to someone like me, who is buried in this stuff all the time.
Writing is so fragile – how did any of these primary sources survive? An excellent question. The quickest answer is that everything was written on a surprisingly robust medium, which was then stored away and forgotten. Survival!
Virtually all of our primary source material was written down on vellum, which is calf skin that has been treated and stretched. This material is far more robust than paper, which in any case didn’t make it to western Europe until the eleventh century. Early medieval scribes used two types of inks, one based in carbon and one in iron. Both produced a rich, long-lasting dark lettering. The manuscripts were bound with heavy leather or even wood, when the manuscript was particularly valuable. As long as you keep the manuscript reasonably dry, protected from rats, and away from flames, it will last a long time.