About 810 Frankish Benedictine monk, Hrabanus (Rabanus) Maurus, wrote De laudibus sanctae crucis, a collection of 28 encrypted religious poems in praise of the holy cross. Arranged in the carmina figurata style of word pictures, in which shapes appropriate to the textual context are created by the outlines of letters, phrases or verses of poetry, these became much-admired and often copied. Maurus eventually became archibishop of Mainz.
In February 2014 a digital facsimile of an excellent 11th century illuminated manuscript of the text was available from the Burgerbibliothek, Bern, Switzerland at this link.
Bischoff, Latin Paleography: Antiquity and Middle Ages (1990) 210.