Unlike modern calendars, with their grids of empty days ready to be filled with engagements, medieval calendars came chock-a-block with data—to fill you in. The first two columns in this month of May (Maius, written at the top left) contain Golden Numbers and Dominical Letters for identifying the date of Easter, a movable feast. The next two columns contain the Roman calendar, with three fixed days: the Kalends (KL), Nones (Nonas), and Ides (Idus). Last come the feast days, the most important of which are written in red (hence our expression “red-letter day”); May 1 is the high feast of Saints Philip and James (Philippi et Iacobi). The month is illustrated with frolicking dragons and its particular Labor (hawking) and Zodiac sign (Gemini).
Psalter, in Latin and Dutch, Netherlands, Utrecht, ca. 1300, MS M.113, fol. 3.urchased by J. Pierpont Morgan (1837–1913), 1907.