The Codex Exilium is a physically enormous volume (approx. 25 lbs) consisting of a series of brass plates recording the rituals used by the generals of the God Valdos (one of the The Lords of the Pentacle) to summon, banish or bind enemy Angels. These generals would have been mortals or angels themselves, and some might have started as the former and been 'promoted' to the latter after some great service (the most famous case, albeit not from the Valdosian armies, is Kirva's archangel, Adarnum (of "Knights of" fame), who was once a mortal king). The rituals in the Codex, however, required the reality-altering language of the Elder Gods.
These plates are "annotated" with supplemental wards and ritual cants discerned by later scholars - one particularly significant improvement came from one of the later Mage Princes who recorded the dictations of an angel of Adalna (the patron God of a major faction of Mage Princes during their civil war and eventual collapse).
The Codex has, at various times, passed through the possession of the following characters and Institutions: