The Calendar of 354 sometimes referred to as the Chronography of 354, was a 4th-century illuminated manuscript, initially created in 354 C.E. for a wealthy Roman Christian named Valentinus, by Furius Dionysius Filocalus. It is the earliest dated codex to have full page illustrations, and was created in the liminal era between the end of Rome and the start of the Christian middle ages.
The Calendar of 354 is known today only by virtue of its copies. It was “rediscovered” in the ninth century, and copies of it were made by and for the Carolingian court; it subsequently spawned or inspired most successive calendars in Europe, and is the direct ancestor of the calendars contained in psalters and books of hours. More specifically, the common announcement at the start of a month in calendars of books of hours that announce the month and the number of days, as in “Januarius h[abe]t dies xxxi”, “January has 31 days” is directly inspired by the Calendar of 354. In much the same way, the inclusion of the signs of the zodiac in the medieval, Christian books of hours is another trait borrowed from the Calendar of 354.[ref]Christopher de Hamel. Meetings with Remarkable Manuscripts: Twelve Journeys into the Medieval World. Penguin Press, 2017. Chapter 12[/ref]
The Calendar of 354 is perhaps best compared to a modern almanac; it was much more than a simple calendar. It included chronological tables and lists, ranging from the dates of Easter, the various Popes, lists of various other rulers (i.e. the Prefects of Rome), and similar information. It also included the signs of the zodiac, allegorical images of the various months, and the specific statement (in a list of Christian martyrs) “VIII kal. Ian. natus Christus in Betleem Iudeae” (“Eighth day before the kalends of January [December 25], Birth of Christ in Bethlehem Judea”); the earliest known association of December 25 with the feast of the birth of Christ.
There is an online English edition of the Calendar of 354.