I have October on the mind today, so I figured I would run with that. Medieval books of hours, much like today’s day planners (if anyone even uses those anymore), often included calendar pages for each month of the year. These weren’t the sort of calendars you might write down your appointments in, however. Instead, they had to do with the timing of the religious days, the appropriate prayers for which were included in the book of hours. Calendar pages were often elaborately-decorated with images of the classical figures associated with each month, the appropriate zodiac signs, the saints whose feasts take place during the month, or with the labors of the month – the traditional farming tasks associated with each month. Calendar pages sometime also appear in psalters and other forms of manuscript.
For more about the calendar pages and other sections of the book of hours, see “Inside a Book of Hours” by the Harry Ransom Center of the University of Texas at Austin.