(more properly Kalendarium). Originally the account-book in which debts were entered. As these debts fell due on the Kalends, the name got its first signification from that fact; coming later to mean a register of the days, weeks, and months. The Greek terms are ἡμερολόγιον and ἐφημερίς.
(1) Greek. The Greek year consisted of twelve monthssome full, i.e. of 30 days each; the others, hollow or incomplete, of 29 days each. This made up a lunar year of 354 days, 11 days short of the solar year. To maintain some correspondence between the lunar and the solar years, and to provide at least for the festivals of the seasons always occurring at the right time of year, the Athenians early resorted to the method of intercalation. A space of time was taken which included as many days as would exactly make up eight solar years, and could easily be distributed among the same number of lunar years. This space of time was called a great year. Then in every third, sixth, and eighth year, a month of 29 or 30 days was inserted, so that the years in question consisted each of 383 or 384 days. This system was introduced at Athens by Solon. The period of eight years was sometimes called ἐνναετηρίς, or a period of nine years, because it began again with every ninth year; sometimes ὀκταετηρίς, or space of eight years. For this the astronomers, of whom Meton (q.v.) in the Periclean Age may be taken as a representative, substituted a more accurate system, which was afterwards adopted in Athens and other cities as a correction of the old calendar. This was the ἐννεακαιδεκαετηρίς of nineteen years. The alternate full and hollow months were divided into three decades, consisting of 10 or 9 days each, as the case might be. The days of the last decade were counted from more to less to correspond with the waning of the moon. Thus the 21st of the month was called the 10th of the waning moon, the 22d the 9th, the 23d the 8th, and so on. The reckoning of the year, with the order and names of the months, differed more or less in different States, the only common point being the names of the months, which were almost without exception taken from the chief festivals celebrated in them. The Athenians and the other Ionian peoples began their year with the first new moon after the summer solstice, the Dorians with the autumnal equinox, the Boeotians and other Aeolians with the winter solstice. The table given below shows the succession of the Attic months, the number of days they contained, and the corresponding months of our year.
At the time when the Calendar Julian was adopted by the Athenians, probably about the time of the emperor Hadrian, the lunar year appears to have been changed into the solar year; and it has further been conjectured that the beginning of the year was transferred from the summer solstice to the autumnal equinox. The intercalary month was a second Poseideon inserted in the middle of the year. The official system of numbering the years differed also very much in the various States. The years received their names from the magistrates, sometimes secular, sometimes spiritual. (See Eponymus.) Historical chronology was first computed according to Olympiads, or periods of four years, beginning B.C. 776, by the historian Timaeus in the third century B.C.
(2) Roman. The Roman year was supposed to have consisted, under Romulus, of 10 months four full ones of 31 days (March, May, July, and October) and six hollow of 30 days (April, June, August, September, November, December). But, as a space of 304 days makes up neither a solar nor a lunar year, it is difficult to understand the so-called year of Romulus. King Numa was popularly supposed to have introduced the year of 12 months by adding January and February at the end; for the Roman year, it must be remembered, began originally with March. By this system every month except February had an odd number of days: March 31, April 29, May 31, June 29, Quintilis 31, Sextilis 29, September 29, October 31, November 29, December 29, January 29, February 28. Numa is also credited with the attempt to square this lunar year of 355 days with the solar year of 365; but how he did it is not certainly known. The Decemviri in B.C. 450 probably introduced the system of adjustment afterwards in use. According to this, a cycle of four years was taken, in the second year of [figure in text: Roman Calendar, with Copy of Inscription for January. (Pompeii.)] which an intercalary month (mensis mercedonius) of 23 days was inserted between the 24th and 25th of February, and in the fourth year a month of 22 days between the 23d and 24th of February. [p. 255]
Thus the period of four years amounted to 1465 days. But this gave the year an average of 366 1/4 days, or one day too many, so that a special rectification was necessary from time to time. This was probably carried out by the omission of an intercalary month. It was the business of the pontifices to keep the calendar in order by regular intercalation; but, partly from carelessness, partly from political motives, they made insertions and omissions so incorrectly as to bring the calendar into complete confusion, and destroy the correspondence between the months and the seasons. The mischief was finally remedied by Iulius Caesar, with the assistance of the mathematician Sosigenes. To bring the calendar into correspondence with the seasons, the year B.C. 46 was lengthened so as to consist of 15 months, or 415 days, and the calendar known as the Julian was introduced on the 1st of January, B.C. 45. This calendar is founded simply on the solar year, which is well known to be a discovery of the Egyptians. Caesar fixed this year at 365 1/4 days, which is correct within a few minutes. After this, the ordinary year consisted of 365 days, divided into 12 months, with the names still in use. Every fourth year had 366 days, a day being inserted at the end of February. The Julian Calendar maintained its ground till 1582, when Pope Gregory XIII. corrected the trifling error which still attached to it. The old names of the months were retained with two exceptionsthat of Quintilis, which, in honour of Iulius Caesar, was called Iulius, and that of Sextilis, which in B.C. 8 was called Augustus, in honour of the emperor. The old divisions of the lunar month were also retained for convenience of dating. These were (a) the Kalendae, marking the first appearance of the new moon; (b) the Nonae, marking the first quarter; (c) the Idus, marking the full moon. Kalendae means properly the day of summoning, from calare, to summon. The pontifex was bound to observe the first phase, and to make his announcement to the Rex Sacrorum, who then summoned the people to the Capitol, in front of the Curia Calabra, so called from calare. Here he offered sacrifice, and announced that the first quarter would begin on the fifth or seventh day (inclusive) as the case might be. This day was called Nonae, as (according to Roman calculation) the ninth day before the full moon, and fell in March, May, July, and October on the 7th, in the other months on the 5th. The appearance of the full moon was called Idus (probably connected with the Etruscan word iduare, to divide), because it divided the month in the middle. The days of the month were counted backwards, in the first half of the month from the Nones and Ides, in the last half from the Kalends of the following month. The Romans also had a week called internundinum, or the interval between two nundinae. It consisted of eight days, and, like our weeks, could be divided between two months or two years. See Fasti.
After the establishment of the Republic the Romans named their years after the consuls, a custom which was maintained down to the reign of Justinian (A.D. 541). After the time of Augustus it became the practice in literature to date events from the foundation of Rome, which took place, according to Varro, in B.C. 753; according to Cato , in 751.
The Day.The Greeks reckoned the civil day from sunset to sunset, the Romans (like ourselves) from midnight to midnight. The natural day was reckoned by both as lasting from sunrise to sunset. The divisions of the day were for a long time made on no common principle. It was for military purposes that the Romans first devised such a principle, dividing the night during service into four equal watches (vigiliae). Corresponding to this we find another division (probably calculated immediately for the courts of justice) into mane (sunrise to 9 or 10), forenoon (ad meridiem), afternoon (de meridie) until 3 or 4, and evening (suprema) from thence till sunset. After the introduction of sundials and waterclocks, the day and night were divided each into twelve hours; but the division was founded on the varying length of the day, so that each hour of the day was longer, and conversely each hour of the night shorter, in summer than in winter.
It should be observed that several of the Eastern nations, for the purpose of preventing confusion in their calculations with other nations, dropped the names of their months, and merely counted the months, as the first, second, third, etc., month. For extended information see Corsini, Fast. Att., which, however, is very imperfect; Ideler, Handbuch der mathem. u. technischen Chronol. (Berlin, 1826); Clinton, Fast. Hellen. vol. ii. Append. xix.; and more especially K. F. Hermann, Ueber griechische Monatskunde (Gttingen, 1844); Bergk, Beitrge zur griechischen Monatskunde (Giessen, 1845); Boeckh, Ueber die vierjhrigen Sonnenkreise der Alten (Berlin, 1863); Mommsen, Chronologie (Leipzig, 1883); Ideler's work, Lehrbuch der Chronologie, 2 vols. (Berlin, 1826); Mommsen, Die rmische Chronologie (Berlin, 1858); and Matzat, R. Chronologie, 2 vols. (Berlin, 1883). For further information connected with the ancient measurement of time see the articles Astronomia; Dies; Horologium; Lustrum; Nundinae; Saeculum; Vigiliae.