On the 5th day before the calends of October (Sept.
The number of days receiving their denomination from the Calends depended on the number of days in the month and the day on which the Ides fell.
February Having Then Twenty Nine Days, The 25Th Was The 6Th Of The Calends Of March, Sexto Calendas; The Preceding, Which Was The Additional Or Intercalary Day, Was Called Bis Sexto Calendas, Hence The Term Bissextile, Which Is Still Employed To Distinguish The Year Of 366 Days.
The civil year commenced with the calends of January, but this did not hold a fixed place in the solar year till the time of Julius Caesar(see Calendar).
From these three terms the days received their denomination in the following manner: - Those which were comprised between the Calends and the Nones were called the days before the Nones; those between the Nones and the Ides were called the days before the Ides; and, lastly, all the days after the Ides to the end of the month were called the days before the Calends of the succeeding month.
In January, therefore, the 14th day of the month was called the nineteenth before the Calends of February (counting inclusively), the 15th was the 18th before the Calends and so onto the 3 0 th, which was called the third before the Calend (tertio Calendas), the last being the second of the Calends, or the day before the Calends (pridie Calendas).