The creator of the Roman calendar was the legendary founder of Rome - Romulus (VIII c. p.n.e.). The natural year was the basis, based on observations of certain phenomena in the animal and plant world. It consisted of 10 months. Six of them had po 30, and four - after 31 days. The Roman - Romulus year - thus counted only 304 days. It was beginning 1 III. The arrangement of the months was as follows:
Martius - March - dedicated to the god of war, Mars, "Father" of Romulus
April Fools - April - dedicated to Venus (Aphrodite)
Maius - May - the month of Maya, goddess identified with Bona Dea
Iunius - June - the month of Juno
Quinctilis - July - fifth in a row
Sextilis - August - the sixth
Semptember - September - the seventh
October - October - eighth
November - November - ninth
December - December - the tenth
Such a calendar could not, of course, last long. Therefore - with the achievement of a higher degree of civilization development - the lunar calendar was introduced with the month as the most important unit of time. When it happened - it is not known. The Romans argued, that this was done by Romulus' successor, Numa Pompilius. Others - that the god Janus himself, creator of Heaven and Earth, father of all other gods and people, also the god of time (by the way - the only native Roman god in the pantheon of gods imported from Greece). Either way - it was an important reform.
The year of Numa (or Janus) consisted of 12 months. Four of them (III, V, VII and X) had po 31 days, seven months (IV, WE, VIII, IX, XII and I) after 29, one month (II) — 28. Roman year, according to this calendar, so he was already counting 355 days.
Of course, it was far from being compatible with the solar year. To remedy this discrepancy, it was introduced in the 5th century. p.n.e. leap years, with additional months after 22 the 23 days (the so-called. Mercedonius), and posted every other year after the February terminology holiday, i.e. between 23 a 24 February. These months occurred in a 4-year cycle, wherein 2 the years were ordinary, counting after 355 days, i 2 leap years: one - counting 377 days (355 + 22), second - 378 (355 + 23). The sequence of years in the cycle was as follows: 355 + 377 + 355 + 378. The total number of days was thus in the cycle 1465, the average length of the year 366,25 day.
As it follows, The Romans exaggerated. Anyway, no wonder: in astronomy and mathematics they were not strong. They probably did not know the true length of the solar year yet.
Added 2 months bore names: January and February. They were inserted into the calendar not after the tenth month - December - but at the beginning, so before March, dedicated to Mars. Ianuarius was the month of Janus. It was now opening not only the Roman year, but also every month, and even a day. Unfortunately, it was not a perfect calendar. Priests took care of him. The Act of Manius Acilius Glabrion of 191 r. p.n.e. imposed on them the obligation to correctly establish leap years. However, they rarely lived up to it. As a result, the calendar was in chaos. It was only the reform of Julius Caesar that put an end to this, introducing new calendar based on the solar count of time.
And since the years were counted?
In Republican Rome, a system of determining the year according to the names of both consuls was maintained, so similar to Athens (according to the archon) and in Sparcie (ephora). It was written e.g.. "For the consulate of Marek Messala and Marek Pizon". The starting point was the date of the foundation of Rome, but finding it was difficult. Only the Roman encyclopedist did it, Marcus Varro z Beate (116—27/26 p.n.e.). He took a year 753 p.n.e. (according to our conversion) as the foundation year of Rome. This date was widely recognized as the beginning of the Roman era, but… only in historical and literary chronology. Pisano: ab urbe condita - since the founding of the city. Sometimes there was also a dating system from… the expulsion of the kings from Rome, what - according to Roman historians - happened approx. 510 r. p.n.e. Every day - in official and private chronology - they were dated in the old way: according to the names of the consuls in office or the years of the rulers' rule.