And keeping track of calendars was part of their job!!
>The Pontifices were in charge of the Roman calendar and determined when intercalary months needed to be added to synchronize the calendar to the seasons. Since the Pontifices were often politicians, and because a Roman magistrate's term of office corresponded with a calendar year, this power was prone to abuse: a Pontifex could lengthen a year in which he or one of his political allies was in office, or refuse to lengthen one in which his opponents were in power. A Pontifex with other political responsibilities, especially away from Rome, might also have been simply distracted from his calendrical duties as chief priest. This caused the calendar to become out of step with the seasons; for example, Caesar's crossing of the Rubicon in January 49 BC actually took place in mid-autumn.
Under his authority as pontifex maximus, Julius Caesar introduced the calendar reform that created the Julian calendar, with a fault of less than a day per century, and which remained the standard till the Gregorian reform in the 16th century.
https://en.wikipedia.org/wiki/Pontifex_maximus#Roman_Republi...