Sentence:  The Romans did not, as we do, count the days of the month in a regular numerical succession, but reckoned them with reference to three principal points of time—the <WSD>Calends</WSD>, the Nones, and Ides. The first day of every month was entitled its <WSD>Calends</WSD>. [...] The <WSD>Calends</WSD> were originally the day of the new moon, which received its name from the fact that on that day the Pontifex addressed the moon in presence of the people, in the words "Calo te, Jana Novella," "I call upon thee, new moon," which was repeated as many times as intimated to his hearers the number of days before the arrival of the Nones. 
Meaning of the word marked with <WSD> tags:  "Often with initial capital": the first day of a month, particularly  the first day of a month of the Roman calendar.