We now number the days of the month from 1 up to 28, 29, 30, or 31. Days have not always been identified in this humdrum way. Romans designated each day by the number of days before certain fixed days in the month, which were called the Kalends, the Nones, and the Ides. Dates were a countdown to these days. The Kalends were the first day of the month, the Nones the fifth, and the Ides the thirteenth -- except in March, May, July, and October, when the Nones and Ides were two days later. Weeks did not come into the scheme, as indeed they do not in the current scheme.
The day after the Ides of March was the 17th before the Kalends of April, written die XVII a.d. Kal. Aprilis. Kalends is one of the few Latin words retaining the K from the early alphabet. That the Ides were usually the thirteenth day of the month might be thought the origin of the unlucky connotation of the number 13, but this is not so, and there is nothing generally sinister about the Ides. Julius Caesar's fatal Ides of March were on the 15th, not the 13th, and nobody numbered days of the month serially anyway.
Now March has 31 days, so the number of days after the Ides is 31 - 15 = 16, not 17. In counting an interval of discrete items, Romans always included the first and last, so the Kalends of April was the 17th day after the Ides of March. This counting habit caused confusion when the Julian calendar was first introduced. Sosigenes, the astronomer behind the calendar, had said that every fourth year was to be a leap year. The officials in charge of the calendar added the extra day every third year for a while. This was sorted out by Augustus, and the Julian calendar has been uniform since then. Several of the months were renamed later, Quintilis and Sextilis becoming July and August.
Roman day numbering replaced the old, very confusing lunisolar calendar that introduced days at various times depending on religious demands and the phases of the moon. By the time of the reform in 46 BC, this calendar had lost all correlation with the seasons and the moon. The moon has been banished from Julian and Gregorian calendars because of its maddening incommensurability. This was first done in Egypt in 4241 BC, when the year was divided into 12 30-day months plus 5 intercalary days for a festival at the year's beginning. The Egyptian year began with the simultaneous rising of the Sun and Sirius in midsummer, at the time of the annual rise in the Nile. This calendar was the basis for Sosigenes's reforms. The reason for the extra 31-day months in the summer in the Julian calendar is that the sun moves slightly more slowly in the summer along the ecliptic.
Roman years were identified by the names of the two consuls elected for that year. For historical purposes, years were numbered from the traditional date of the founding of Rome, 753 BC. In the Principate, laws and other official actions were dated by the year of reign, a practice that continues to the present day in England, for example. The Roman style of dates is preserved in spirit in some localities by expressing the days until a saint's feast day.
The introduction of the Gregorian calendar at the end of the sixteenth century finally encouraged uniformity in dating. The only changes made in the Julian calendar were the elimination of leap days every century (unless divisible by 400), and a shift of eleven days to get the calendar back into the same relation with the vernal equinox that it had when introduced.
Roman years began in January, as do ours, but somehow the habit arose of beginning the year with the vernal equinox, in March (this was also the beginning of the year in the ancient lunisolar calendars). The Gregorian calendar began the year with January again. Until the Gregorian calendar became adopted in Protestant as well as Catholic countries, the confusion of the beginning of the year and the shift of days brings excitement to historical dating.
Galileo Galilei died on 8 January 1642, and Isaac Newton was born on 25 December 1642 (O.S. = old style). A. Wolf remarks on page 38 of his History of Science, Technology and Philosophy in the 16th and 17th Centuries that these events happened in the same year, and others have suggested some superstitious significance to the fact. On the Gregorian calendar, Newton's birth occurred 4 January 1643. The year is different now, but he did succeed in being born in the same interval of 365 days after Galileo died, by four days.
The origin of the numbering of our years was arbitrary, the work of a superstitious, bumbling ecclesiastic, and arising sometime in the fourth century. Whether there was year zero or not has nothing to do with the question. Usually the year before 1 AD is called 1 BC, but astronomers call it year 0. 1 January 2000 is the day the year changes from 1999 to 2000, but nothing else. 1 January 2001 is equally devoid of significance, being the start of the 2000th year after some arbitrary year. The greatest influence of the year 2000 is its effect on bad computer programs.
Composed by J. B. Calvert
Created 20 July 1999