Calends, Nones and Ides

At the time of their early kings, Roman months were of a length identical to the lunar cycle. Each month was divided into sections that ended on the day of one of the first three phases of the moon: new, first quarter or full. 1  All days were referred to in terms of one of these three moon phase names, Calends, Nones or Ides.
At that time a pontifex (priest) was assigned to observe the sky. When he first sighted a thin lunar crescent he called out that there was a new moon and declared the next month had started.2   For centuries afterward, Romans referred to the first day of each month as Kalendae or Calends from the Latin word calare (to announce solemnly, to call out). 3   Obviously, the word calendar was derived from this custom.

Of the three sections, Calends was the longest—it had more days than the other two combined. That’s because it spanned more than two lunar phases, starting from the day after full moon and continuing thru its last quarter and waning period, then past the dark new moon until another lunar crescent was sighted. The day of Calends itself began a new month. It was dedicated to Juno, a principal goddess of the Roman Pantheon.
Unnamed days in the early Roman month were assigned a number by counting down following the day of each named phase, day by day, ending with the next of those three phases. The first numbered day in each section had the section’s highest value. Each succeeding day was one number lower than that of the day before. (Similar to the modern count-down when coordination of a group of people is required for a complicated activity such as launching a rocket.)

Latin for “the evening before” is “Pridie,” a word that was used to refer to the day before each of these named phases. So Pridie was always the day that would otherwise have been numbered two. The count-down was inclusive; the day from which they started as well as that of the moon phase to which they were counting down, day one, were both included. 4
Nones (Latin nonus or ninth) was originally the day when the moon reached its first quarter phase. 5   When the pontifex initially saw the lunar crescent he noted its width and, using empirical knowledge, calculated the number of days that were expected to elapse between then and the first quarter moon. He then specified that number after he announced the new crescent. If he called out the number six, the day following Calends would be referred to as the sixth day before Nones.
In any given year, the second day of Martius might well have been designated as the sixth of the Nones of March: “ante diem VI Non. Mart.” If this were the case, Nones would be the seventh day and Ides would be the 15th day of that month. The difference between these two dates, eight days, was always the length of the Ides section.
Use of the word “Nones” (nine) was intended to express the inclusive number of elapsed days between first quarter and full moons. Actually, the time between moon phases now averages about 7.4 days, but they sometimes occur eight days apart. Eight-day separations of first quarter and full moons now usually come grouped in consecutive lunations. They then give way to mostly seven-day periods.

Six of the first seven lunations of 1997, for instance, had their first quarter and full moon phases eight days apart (inclusive nine-day spans). Also, July 1 of 1998 had a first-quarter moon followed by a new moon on July 9, a nine-day period. 6   This helps explain why the unlikely term of Nones, meaning ninth, was used to designate one fourth of the moon’s period that now averages about 29.53 days.
Ides, dedicated to Jupiter, was originally the time of the full moon. Because a full moon comes halfway thru each lunation, its day was called Idus in Latin from an Etruscan word meaning “divide.”

After Ides, the next new moon was expected to appear in from 15 to 17 days. Variations in the length of time before another new moon can be sighted is due to constantly changing positions of moon and Earth relative to the sun.
Romans separated their months from the lunar cycle in the fifth century B.C. Month lengths then became fixed. At that time, Ides was assigned as the 15th day in all months given 31 days in length—March, May, July and October. It was designated as the 13th day in all other months. As a result, from then on the Calends section had from 16 to 19 days, the Nones section had either four or six days and the Ides section, as before, always had eight days.

Sometime after Calends, Nones and Ides were fixed on predetermined days of the month rather than being defined by phases of the moon, Romans used letters A thru H on the left side of each month’s calendar column to indicate days of their eight-day marketing week. The first day of each new year was represented by the letter “A.”
It is both unfortunate and ironic that the first Caesar was assassinated on the Ides of March in the year 44 B.C.
You can see a pre-Julian calendar’s first three months at  Early Roman Calendars. That type of calendar was used following the time that months were identical with lunations.

(1) Key, Thomas Hewitt, M.A.,
William Smiths A Dictionary of Greek and Roman Antiquities
London, John Murray, 1875. pp. 226-233
(2) Bickerman, Elias Joseph. Chronology of the Ancient World.
Ithica, N.Y.: Cornell University Press, 1968. p. 17.
(3) Webster’s New World™ Dictionary. Copyright (c) 1994
Compton’s NewMedia, Inc.
(4) Parise, Frank. The Book of Calendars.
New York: Facts On File, Inc. p. 43.
(5) Bickerman. op. cit., p. 44
(6) Osburn, Chris. Lunar Outreach