C. Codex Ephraemi,

now in the National Library of Paris, having been brought from the East to Italy early in the sixteenth century, and taken from Italy to Paris by Queen Catherine de' Medici.
This manuscript is a prominent instance of a fate which befell many ancient books in the Middle Ages, before the introduction of paper into Europe.
When vellum became scarce, a scribe who was unable to procure a sufficiency of it was apt to take some manuscript to which he attached little value, wash or scrape off the ink as well as he could, and then write his book on the vellum thus partially cleaned.
Manuscripts so treated are called palimpsests, from a Greek word implying the removal of the original writing.
The Codex Ephraemi is a palimpsest, and derives its name from the fact that the later writing inscribed upon its vellum (probably in the twelfth century) consists of the works of St. Ephraem of Syria.

Description & picture from 'Our Bible & the Ancient Manuscripts' by Sir Frederick Kenyon (1895 - 4th Ed. 1939) Page 142 & Plate XVIII. (Page selection illustrated: 22.5 x 18cm. Page-size: 30.5 x 24cm. )