Einhard tells us that Charlemagne could not write well (though he kept
a tablet under his pillow to practice with) . This is the typical monogram used
by his chancery. The initials and black cardinal lines were made by the scribe;
Charlemagne drew the square and 'X' at the center with his own hand. His successors
used variants on the monogram; we also see similar monograms on papal documents.