Special sacrifices were offered on the kalends, nones, and ides of every month, and on the occasion of important family events.
Instead of distinguishing the days by the ordinal numbers first,, second, third, &c., the Romans counted backwards from three fixed epochs, namely, the Calends, the Nones and the Ides.
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 the months of March, May, July and October, the Ides fell on the 5th day, and the Nones consequently on the 7th; so that each of these months had six days named from the Nones.
In all the other months the Ides were on the 13th and the Nones on the 5th; consequently there were only four days named from the Nones.