Chock full of information, Calendar pages in Books of Hours were the medieval way of telling time. Written in French, this Calendar page for the month of September begins “September has 30 days” and “the moon is on the 30th.” Feast days in red are the more important ones, the “red letter days.” Here they are Saints Leo and Gilles on September 1, the Birth of the Virgin Mary on September 8, and the Feast of the Holy Cross on September 14. To the left of the feasts are three columns. The first column lists the Golden Numbers, which indicate the appearances of the new moons and the full moons throughout the year. The Dominical Letters (“a” through “g”) in the second column help one find Sundays. The third column includes the ancient Roman calendrical system, listing Ides (“id”) and Kalends (“kl”).