Solar and lunar calendars are both attested in early Jewish literature; but from the first century ce until this very day, the lunar calendar appears to have completely prevailed. The first section of this chapter will trace this apparent transition to an exclusively lunar calendar.
In the second section, an attempt will be made to explain why the Jews abandoned solar calendars around the first century ce. For this purpose, I shall assess the wider historical context in which this development occurred. Jewish calendar reckoning was sometimes influenced by other calendar systems, but sometimes strove to remain distinct. In the Roman period, I shall argue, the lunar calendar became to the Jews a marker of their distinctive communal identity.
The Jewish (and other similar) lunar calendars are usually referred to as 'lunisolar', because they keep up with the annual solar year by adding a 13th lunar month every two or three years; in this respect, these calendars comprise a solar element, which distinguishes them from purely lunar calendars such as the Muslim calendar. However, in this chapter and throughout this book I shall refer to the Jewish calendars as 'lunar', because their solar component is marginal by comparison with their mainly lunar nature. Truly lunisolar calendars, where the lunar and solar elements are more or less on a par, can only be found in Qumran and related sources (see below, sections 1.1.3-6 , where the term 'lunisolar' is frequently used). Moreover, in the context of ancient Jewish calendars the term 'lunisolar' can often be a misnomer, because the addition of a 13th month is not always regulated by the cycle of the sun. As we shall see in Ch. 2 , intercalation of a 13th month in the ancient Jewish lunar calendar was not regulated by the solar year (e.g. by the equinox) but instead by seasonal/agricultural criteria such as ʾaviv, and thus was only indirectly related to the solar year. It should also be noted, finally, that many ancient sources (e.g. rabbinic sources, as will be cited at the end of this chapter) consider the Jewish calendar to be based on the