and concludes that the institution of this calendar can thus be dated precisely
to the reign of Xerxes (486– 465 BCE). Although de Blois allows for some
flexibility, by extending 481– 479 BCEto the entire reign of Xerxes, he still
places excessive confidence in an astronomical argument, which—like all
astronomical arguments—is not without considerableflaws. In 481– 479 BCE,
1 Farwardīn would have occurred on 26 March, which according to modern
astronomical calculation was indeed the date of the true vernal equinox.^35 This
is to assume, however, that the Persians in this period were capable of
calculating the equinox to the same level of precision as modern astronomers,
which is most unlikely.^36 The Persians themselves were not distinguished in
thefield of astronomy (Pingree 1987: 858); if, as is quite possible, they
consulted Babylonian astronomers, they would have been given a date of the
equinox that could be as much as three days later than ours.^37 Furthermore,
and more importantly, this astronomical argument is based on the assumption
that the Persians waited—possibly decades—for theexactcoincidence of the
vernal equinox and the 1st day of an Egyptian month (to be renamed
Farwardīn) before instituting their new calendar. This assumption is unrea-
sonable: it seems far more likely that the new calendar was instituted whenever
the decision to do so was taken, with itsfirst month, Farwardīn, corresponding
to the Egyptian month that was theclosest, at the time, to the vernal equinox.^38
A margin of 15 days on either side of the equinox should therefore be allowed.
The period during which 1 Farwardīn would have occurred on or within 15
days of the vernal equinox, with Cambyses’conquest of Egypt as aterminusa
quo,^39 is fromc.525 to 430BCE. The astronomical argument thus leads to the
conclusion—as is indeed most likely from a historical perspective—that the
Egyptian calendar was introduced in Persia at some point during thefirst
century of Achaemenid rule over Egypt.
(^35) Not 25 March, as erroneously in de Blois (1996) 49. In 482BCE, 1 Farwardīn also coincided
with the true vernal equinox (in this year on 27 March), provided we assume the day unit began
at midnight or at early dawn. All this is based on the model of the Armenian, Sogdian, and
Choresmian calendars, which for reasons explained below are rightly considered by de Blois as
representative of the original Persian Zoroastrian calendar. According to backward calculation of
the later, post-Sasanian Persian Zoroastrian calendar, 1 Farwardīn would have beenfive days
earlier in these years, i.e. 21 March.
(^36) The same assumption pervades the work of Hartner, who argues that the old Avestan,
pre-Zoroastrian calendar was regulated by the precise observation of equinoxes (1979: 8–9,
1985: 748–56), and that the‘Young Avestan’(his term, i.e. Persian Zoroastrian) calendar was
been instituted in 503BCE, when on his reckoning 1 Farwardīn coincided with the vernal
equinox and Babylonian 1 Nisannu (1979: 2–5, 10–14; 1985: 757–72).
(^37) Assuming the Babylonian astronomers used, as in all cuneiform sources, a schematic
calculation such as the later‘Uruk scheme’(see Ch. 2 nn. 124–5). On the difficulty of observing
equinoxes empirically, see A. Jones (2007) 153.
(^38) See further Introduction, near n. 15.
(^39) However, the absence of this calendar in the Behistun inscription suggests that it was not
yet in existence at the beginning of Darius’reign.
178 Calendars in Antiquity