different calendars is bound to haveled to confusion, and although not
intrinsically impossible (it appears to have occurred, for example, in the
Roman province of Arabia and in the Sasanian Empire; seeCh. 5 ), as a
hypothesis it is far from ideal. The absence in Egypt and Babylon of distinctive
month names for their various putative calendars—in contrast to the arch-
ontic and prytanic calendars of Athens, which are wellattested and clearly
distinguished with different monthlengths and month names—raises in fact
the plausibility that in Egypt and Babylon, there never was more than one
calendar. To sum up, the dualor multiplecalendar modelis at best a
complication; it should not be assumed unless there is compelling evidence.
Another well-established belief in ancient calendar studies is that modern
astronomy can enable the date of institution of ancient calendars to be
precisely worked out. Accordingly, the institution of the Egyptian civilcalen-
dar has been dated precisely to 278 1 – 2778 BCE, when modern astronomy tells
us that the Egyptian NewYear coincided with the heliacal(late morning)
rising of the star of Sothis; thePersianZoroastrian calendar was allegedly
instituted in 48 1 – 479 BCE, when its NewYear coincided with the vernal
equinox; and the Jewishfixed rabbinic calendar in the mid-fourth centuryCE
(more precisely, according to one medievaltradition, in 3 59 CE), when the
earliestPassover in the 19 - year cycle coincided with the vernalequinox. These
astronomicalarguments give an impression of scientificreliability and preci-
sion that are rarely achieved in the discipline of history; but in almost allcases,
this impression is onlyillusory. The use of modern astronomy for dating
calendars depends, in fact, on a number of unfounded assumptions:firstly,
that ancient calendars were constructed on the basis of precise astronomical
events (such as the rising of Sothis or the equinox), which in most cases is
actually moot; secondly, that the calendar institutors were able to establish the
dates of these astronomicalevents with a highlevelof precision, and in the
same way as modern astronomers; and thirdly, that the calendars were
instituted at a point in history when they were in optimalalignment with
these astronomicalevents, even if this would have meant waiting along time
for the alignments to occur (this is especiallyrelevant to the institution of the
PersianZoroastrian calendar). The dates when calendars were instituted are
unlikely to have been determined by astronomicalcircumstances: calendars
are far morelikely to have been instituted as and when societies or their rulers
wanted them. As Bickerman wrote on the Egyptian calendar:‘there is no
inherent necessity to start a new calendar on itsfirst day’.^15
Related to these astronomicalarguments is whatIwouldcall‘scientific
reductionism’, which consists in reducing ancient calendars (and hence their
(^15) Bickerman ( 1 968) 4 1 – 2. On the astronomicalargument in the context of the Egyptian and
PersianZoroastrian calendars, seeChs. 3 and 4.In the context of thefixed rabbinic calendar, see
Stern (200 1 ) 197 – 200, 209.
12 Calendars in Antiquity