in Roman antiquity, the first day of each month, so called from the Greek [kalein], to proclaim: it being customary, on those days, to proclaim the number of holy-days in each month.

The Roman method of reckoning the days of their months has something extremely singular in it: instead of computing forwards, in the natural order of the numbers 1, 2, 3, &c., they reckoned backwards, in the manner expressed in the following verses:

Prima dies mensis cuiusque est dicta calendae; Sex Maius, nonas, Julius, October, & Mars; Quatuor at reliqui: habet idus quilibet octo; Inde dies reliques omnes dic effe calendae; Quas retro numerans, dices a mensa sequente.

Hence to find the day of our month answering to that of the calends, to the number of days in the preceding month add two, and from this sum subtracting the number of calends given, the remainder will be the day of our month: thus the fourth of the calends of June is found to answer to the twenty-ninth of May; and so in other cases.