An Ancient 360-day Calendar


This sketch is of a calendar similar to one on a terra cotta block in Rome’s Saint Felicity oratory (pictured near the bottom of this page). 1  Three sets of drilled holes held pegs to indicate day of the week and one of thirty day-numbers for each of twelve months.

  •  Day of the Week
  • Month of the Year
  • Date of the Month
  • Date shown on the Calendar
  • In Rome

Day of the Week

Carved across the block’s top are images representing seven pagan deities: Saturn, Sun, Moon, Mars, Mercury, Jupiter and Venus, left to right in that order. The sequence in which these gods appear is identical with that dictated by the hourly cycle that determined day names, so we know the holes beneath them were used to indicate day of the week. 2

weekday

Once each day the peg beneath a pagan deity would be moved one position to the right. (After the day named for Venus the peg would be moved to the far left under Saturn’s image.) A peg shown on the block in the photo near the bottom of this page is under the fourth image from the left, Mars. It indicates Tuesday, the English word used to name his day. 3

Month of the Year

The large engraved circle beneath day-of-the-week indicators is divided into twelve sectors, each of which represents a month in the calendar year. Zodiac signs indicating the solar year’s progression are positioned counter-clockwise within sectors for each of the twelve months. They are positioned with Aries just right of top center, then proceed counter-clockwise with Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces, in that order.
Twenty-four holes are drilled into that large circle’s circumference, one at the outer end of each radius and one in the center of each sector. A peg was probably positioned at the intersection of a radius and the circumference for the first fifteen days of a month and then moved to the hole between there and the following month’s radius-circumference intersection for the sixteenth thru thirtieth days.

Date of the Month

Fifteen holes are drilled along each side of the block as shown here (from the sketch above). As you can see, between each of those holes and the carved circle in the center is a Roman numeral from one thru fifteen on the left and from sixteen thru thirty on the right. They were used to indicate the date of a month.
The probable reason for thirty of these holes (rather than some other number) is given in a quote attributed to the Midrash Rabbah: “The moon begins to shine on the first of the month and increases in luminance till the fifteenth day, when her orb becomes full; from the fifteenth till the thirtieth day, her light wanes, till on the thirtieth it is not seen at all.” 4 Obviously this calendar (or a prototype) was created when each lunation was considered to be a full thirty days in length.

Date shown on the Calendar

A peg has been inserted on the terra cotta block opposite the Roman numeral for twenty-two. That, combined with a peg on the circle’s circumference just below left center indicates the twenty-second day of a month in which the Sun passed thru the constellation Leo. 5  Currently, the sun passes through Leo at the end of summer, from mid-August through mid-September.

Date shown on the Calendar
A peg has been inserted on the terra cotta block opposite the Roman numeral for twenty-two. That, combined with a peg on the circle’s circumference just below left center indicates the twenty-second day of a month in which the Sun passed thru the constellation Leo. 5  Currently, the sun passes through Leo at the end of summer, from mid-August through mid-September.

In Rome

Even though Roman numerals are shown on the block’s face, this was not an official Roman calendar. That’s apparent because early Romans used an eight-day week, not one of seven days. Also, official Roman calendars never had twelve thirty-day months for a calendar year length of 360 days like the one shown here.
Roman soldiers stationed in Egypt became accustomed to the pagan seven-day week and began to introduce it into their own homeland to replace their eight-day marketing week. Octavian (Caesar Augustus) and succeeding Roman rulers permitted this practice but it wasn’t made official until the emperor Constantine took that step in A.D. 321.
The ancient artifact pictured below represents a rare combination—a seven-day week together with a 360-day calendar year. 6  Most calendars of that length were modified or discarded between the 8th and 4th centuries B.C.

Photo of an ancient 360-day calendar on a terra cotta block:

FOOTNOTES:
(1) McCluskey, Stephen C.
Astronomies and Cultures in Early Medieval Europe
Cambridge: Cambridge University Press, 1998. p. 57 – Figure 10 comments.
(A photo is just above these footnotes.)
(2)  Representations of these seven deities can be ordered sequentially in over five thousand different ways. It’s not a coincidence that they are shown in the exact manner dictated by an Hourly Cycle that Determined Day Names
(3)  “Tuesday” was derived from the old Anglo Saxon day name of Tiwes daeg. (Their name for the planet we know as Mars was “Tiw.”)
(4)  The 30-day lunation-length quote from Midrash Rabbah, together with quotes from over a dozen other ancient sources can be found at this web page. It deals with events that took place just before Moses led the people of Israel out of Egypt.
(5)  The circle’s sector just below left center is occupied by a drawing of Leo, the fourth zodiac image counter-clockwise from Aries.
(6)  Weeks of ten days were observed by Greeks, Egyptians and most other ancient peoples whose calendars contained twelve months of thirty days each. The more recent 360-day French Revolutionary Calendar (A.D. 1793-1806) also had weeks of ten days.