Our calendar is basically that devised by Julius Caesar in 46 BC, with some minor later modifications. But the Romans did not have the seven-day week - basically a Jewish concept. Their complex dating system is explained!

Sundials and water-clocks.



Portable sundial - its ground plan is at (1), the face in perspective at (2), and its elevation at (3). The winter solstice (bruma) is given as the eighth day before the calends of January, that is 23 December, and the summer solstice (solstitium) as the eighth day before the calends of July, ie 22 June. (From Cyril Bailey, The Legacy of Rome, Clarendon Press 1923)

The reformed calendar which Julius Caesar instituted in 46 BC enabled the traditional agricultural year, based on the circuit of the earth round the sun, to be reconciled with the revolution of the moon round the earth. His year of 365 days (366 every fourth year) consisted of seven months of 31 days, four of 30 days, and one of 28 days (29 every fourth year).

A slight, and temporary, adjustment had to be made in the time of Augustus, when it was discovered that the pontifices had misinterpreted the instructions and decreed a leap year every three years instead of four. The year was still actually 11 minutes 14 seconds too long, which it remained until Pope Gregory XIII in the sixteenth century corrected the error and adjusted the incidence of the leap year so that it does not fall on the opening year of a century unless that year is divisible by 400. Thus the year 2000 was a leap year; 2100 will not be.

Each month was divided into three parts by three special days: kalendae (the calends) always fell on the first day of the month; idus (the ides) signified the notional day of the full moon, and was the 15th day of March, May, July, and October - the months of 31 days - and the 13th of all the rest; nonae (the nones) occurred on the 9th day before the ides in each case, including in the calculation the day at each end of the period. Thus the nones of March was 7 March, that is the 9th day before the ides. A date was always reckoned according to the number of days it fell before the next special day, both that day and the special day being included in the calculation. Thus 16 March was known as “the 17th day before the calends of April”.

Certain days were given over to religious and other festivals and celebrations, almost all of which took place on dates of an uneven number, which was regarded as being lucky. Other days were designated fasti, indicating that civil and judicial business could be conducted: comitales, on which a meeting of an assembly could be held: and nefasti, on which neither could take place. The Romans worked an eight-day week, the eighth day by our reckoning, the ninth by theirs, being nundinae; it was the day on which traditionally the farmers downed tools and went to market.


Water clock described by Vitruvius (fl. c. 50 - 26 BC). From the tank (A) water drips at a uniform rate through the small pipe (B) into the reservoir (C), in which is a float (D). Shaft (E) is attached to the upper surface of the float. As it rises, its teeth rotate the cog-wheel (F), to which is attached a hand, the position of which indicates the hour on the front of the dial. (From Cyril Bailey, The Legacy of Rome, Clarendon Press 1923)

The Roman day was divided into twelve hours of equal length, from sunrise to sunset, and likewise during the night. Thus the length of an hour, and the hour itself, varied according to the season of the year. The ninth hour of the day gave its name to Nones, a church service held at about 1500 hours; at some point in the Middle Ages this was brought forward to the sixth hour, that is about 1200. The name Nones persisted, however, and gave the word “noon” its meaning of the middle hour of the day. So when we speak of a.m., we mean ante meridiem (before the middle of the day); p.m. is post meridiem (after the middle of the day). Sundials or water-clocks, or a combination of both, were employed to tell the hour.


More on the Roman Calendar

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