Rosh Hodesh (New Moon)

In ancient Israel, as in Egypt and Mesopotamia, New Moon Day (Rosh Hodesh) was of special significance for calendar reasons. This was the day proclaimed as the start of the month. In Israel and within the Babylonian Diaspora, the commencement of each new month was customarily announced by signalfires, and later by messengers. It was a feastday on which celebratory gatherings and sacrifices were held and work forbidden.
When a fixed calendar based on astronomical principles was introduced in the 4th century, New Moon Day lost much of its significance. Only a few features of the original festival have survived.