Onyx cameo set in MS cover

The drawing shows a border (perhaps Medieval or earlier) with settings for gems, in which an antique cameo has been set. This portrays five members of the Imperial family (identity unknown, Augustus is suggested) above two eagles. It was inserted into the cover of a MS copy of the Gospels presented by either Charlemagne or his sister Ada to the Abbey of St Maximin near Treves (Trier).