The Purple Codex
a.k.a. the Coronation Gospels, this is a manuscript of the gospels—written and illustrated in gold ink on purple-stained parchment—made around 795CE in Aachen for the court of Charlemagne.
It became an important part of coronation ceremonies at least from the 12th century onward (the new king / emperor would swear oaths on it); this magnificent gilded silver cover was made for it around 1500CE, to further show off its importance.