The letters _a d_ are often, through error, written together, and so confounded with the preposition _ad_ which would have a different meaning, for _ad kalendas_ would signify _by_, i.e. _on or before the kalends_. The letters are in fact an abridgment of _ante diem_, and the full phrase for “on the second of January,” would be _ante diem quartum nonas Januarias_. The word _ante_ in this expression seems really to belong in sense to _nonas_, and to be the cause why _nonas_ is an accusative. Whether the phrase _kalendae Januarii_ was ever used by the best writers is doubtful. The words are commonly abbreviated; and those passages where Aprilis, Decembris, &c. occur are of no avail, as they are probably accusatives. The _ante_ may be omitted, in which case the phrase will be _die quarto nonarum_. In the leap year (to use a modern phrase), the last days of February were called,-- Feb. 23. a. d. VII. Kal. Mart. Feb. 24. a. d. VI. Kal. Mart. posteriorem. Feb. 25. a. d. VI. Kal. Mart. priorem. Feb. 26. a. d. V. Kal. Mart. Feb. 27. a. d. IV. Kal. Mart. Feb. 28. a. d. III. Kal. Mart. Feb. 29. Prid. Kal. Mart. In which the words _prior_ and _posterior_ are used in reference to the retrograde direction of the reckoning. From the fact that the intercalated year has two days called _ante diem sextum_, the name bissextile has been applied to it. The term _annus bissextilis_, however, does not occur in any classical writer, but in place of it the phrase _annus bissextus_.--The names of two of the months were changed in honour of Julius Caesar and Augustus. Julius was substituted for Quinctilis, the month in which Caesar was born, in the second Julian year, that is, the year of the dictator’s death, for the first Julian year was the first year of the _corrected_ Julian calendar, that is, B.C. 45. The name Augustus in place of Sextilis was introduced by the emperor himself in B.C. 27. The month of September in like manner received the name of Germanicus from the general so called, and the appellation appears to have existed even in the time of Macrobius. Domitian, too, conferred his name upon October; but the old word was restored upon the death of the tyrant.--The Julian calendar supposes the mean tropical year to be 365 d. 6 h.; but this exceeds the real amount by 11′ 12″, the accumulation of which, year after year, caused at last considerable inconvenience. Accordingly, in the year 1582, Pope Gregory XIII. again reformed the calendar. The ten days by which the year had been unduly retarded were struck out by a regulation that the day after the fourth of October in that year should be called the fifteenth; and it was ordered that whereas hitherto an intercalary day had been inserted every four years, for the future three such intercalations in the course of four hundred years should be omitted, viz., in those years which are divisible without remainder by 100, but not by 400. Thus, according to the Julian calendar, the years 1600, 1700,