Leaf on vellum from a printed Book of Hours.

Large initials hand painted in Paris by Hardouin, who had his workshop near the Notre Dame. At the end of the Middle Ages the art of printing was used for Books of Hours, but the appearance of the books had to be much like the manuscript editions of the ages in the past: the letters were copied from the scribes and lines were drawn to write on!
Around the text is an architectural border and very vivid metal cuts: biblical stories [ beheading of John the Baptist? ], hunting scenes, fabulous animals and dancing people.
The text has the calendar for the months of March [ Martius ] and April [ Aprilis] at the top we find the number of days and the number of nights with moonshine!
In March we see the Annunciatio [ nine months before Christmas ] and in April the feastday for the evangelist Mark.
A liturgical calendar showing feast days of the church year, both fixed, like Christmas, and ?movable? (depending on cycles of the moon), like Easter. Important feast days were written or printed in red ink, hence the expression, "red-letter day."