Before Caesar's reform of the Calendar (B.C. 46), the Roman year consisted of 355 days: March, May, Quíntílis (July), and October having each 31 days, February having 28, and each of the remainder 29. As this calendar year was too short for the solar year, the Romans, in alternate years, at the discretion of the pontificés, inserted a month of varying length (ménsis intercláris) after February 23, and omitted the rest of February. The ``Julian Year,'' by Caesar's reformed Calendar, had 365 days, divided into months as at present. Every fourth year the 24th of February (VI. Kal. Márt.) was counted twice, giving 29 days to that month: hence the year was called bissextílis. The month Quíntílis received the name Iúlius (July), in honor of Julius Caesar; and Sextílis was called Augustus (August), in honor of his successor. The Julian year (see below) remained unchanged till the adoption of the Gregorian Calendar (A.D. 1582), which omits leap-year three times in every four hundred years.
 631. Dates, according to the Roman Calendar, are reckoned as follows: -
a. The first day of the month was called Kalendae (Calends).
NOTE: Kalendae is derived from caláre, to call, - the Calends being the day on which the pontiffs publicly announced the New Moon in the Comita Caláta. This they did, originally, from actual observation.
b. On the fifteenth day of March, May, July, and October, but the thirteenth of the other months, were the Ídús (Ides), the day of Full Moon.
c. On the seventh day of March, May, July, and October, but the fifth of the other months, were the Nónae (Nones or ninths).
d. From the three points thus determined, the days of the month were reckoned backwards as so many days before the Nones, the Ides, or the Calends. The point of departure was, by Roman custom, counted in the reckoning, the second day being three days before, etc. This gives the following rule for determining the date: -
If the given date be Calends, add two to the number of days in the month preceding, - if Nones or Ides, add one to that of the day on which they fall, - and from the number thus ascertained subtract the given date. Thus, -
NOTE: The name of the month appears as an adjective in agreement with Kalendae, Nónae, Ídús.
For peculiar constructions in dates, see § 424.g.
e. The days of the Roman month by the Julian Calendar, as thus ascertained, are given in the following table: -
In the third century B.C. the as was gradually reduced to onehalt of its original value. In the same century silver coins were introduced, - the dénárius and the séstertius. The denarius = 10 asses; the sestertius = 2.5 asses.
NOTE: The word séstertius is a shortened form of sémis-tertus, the third one, a half. The abbreviation |-| or HS = duo et sémis, two and a half.