Cæsar gave the strictest injunctions to Sosigenes, a celebrated Alexandrian astronomer whom he brought to Rome for this purpose; and on the same principles Flavius was ordered to compose a new calendar, in which all the Roman fêtes were entered—following, however, the old method of reckoning the days from the calends, nones, and ides. Antonius, after the death of Cæsar, changed the name of Quintilis, in which Julius Cæsar was born, into the name Julius, whence we derive our name July. The name of Augustus was given to the month Sextilis, because the Emperor Augustus obtained his greatest victories during that month.
Tiberius, Nero, and other imperial monsters attempted to give their names to the other months. But the people had too much independence and sense of justice to accord them such a flattery.
The remaining months we have as they were named in the days of Numa Pompilius.
Fig. 57.—The Roman Calendar.
A cubical block of white marble has been found at Pompeii which illustrates this very well.
Each of the four sides is divided into three columns, and on each column is the information about the month. Each month is surmounted by the sign of the zodiac through which the sun is passing. Beneath the name of the month is inscribed the number of days it contains; the date of the nones, the number of the hours of the day, and of the night; the place of the sun, the divinity under whose protection the month is placed, the agricultural works that are to be done in it, the civil and ecclesiastical ceremonies that are to be performed. These inscriptions are to be seen under the month January to the left of the woodcut.
The reform thus introduced by Julius Cæsar is commonly known as the Julian reform. The first year in which this calendar was followed was 44 B.C.
The Julian calendar was in use, without any modification, for a great number of years; nevertheless, the mean value which had been assigned to the civil year being a little different to that of the tropical, a noticeable change at length resulted in the dates in which, each year, the seasons commenced; so that if no remedy had been introduced, the same season would be displaced little by little each year, so as to commence successively in different months.
The Council of Nice, which was held in the year 325 of the Christian era, adopted a fixed rule to determine the time at which Easter falls. This rule was based on the supposed fact that the spring equinox happened every year on the 21st of March, as it did at the time of the meeting of the Council. This would indeed be the case if the mean value of the civil year of the Julian calendar was exactly equal to the tropical year. But while the first is 365·25 days, the second is 365·242264 days; so that the tropical year is too small by 11 minutes and 8 seconds. It follows hence that after the lapse of four Julian years the vernal equinox, instead of happening exactly at the same time as it did four years before, will happen 44 minutes 32 seconds too soon; and will gain as much in each succeeding four years. So that at the end of a certain number of years, after the year 325, the equinox will happen on the 20th of March, afterwards on the 19th, and so on. This continual advance notified by the astronomers, determined Pope Gregory XIII. to introduce a new reform into the calendar.