They were formerly dated by kalends and from the era of the Incarnation, which begins on the 25th of March, but in 1908 Pius X.
CALENDAR, so called from the Roman Calends or Kalends, a method of distributing time into certain periods adapted to the purposes of civil life, as hours, days, weeks, months, years, &c.
The Calends, (or Kalends) were invariably the first day of the month, and were so denominated because it had been an ancient custom of the pontiffs to call the people together on that day, to apprize them of the festivals, or days that were to be kept sacred during the month.
Special sacrifices were offered on the kalends, nones, and ides of every month, and on the occasion of important family events.
The celebrations are directly traceable to the pagan Saturnalia of ancient Rome, which in spite of the conversion of the Empire to Christianity, and of the denunciation of bishops and ecclesiastical councils, continued to be celebrated by the people on the Kalends of January with all their old licence.