Avoidance of an over-rigid pattern (such as the 2½-year scheme) in the
reigns of Nebuchadnezzar and his successors enabled a more accurate luniso-
lar synchronism than under Nabopolassar, although intercalations were still
slightly excessive.^104 It is questionable, however, whether this slight excess
would ever have been noticed. In the absence of anyfixed pattern or cycle (e.g.
of 19 years), it would have been difficult to track the long-term progress of the
calendar year in relation to the seasons. Only obvious excesses would have
been noticed and corrected: for example, in 552 Nisannu began excessively
late, a whole month after the vernal equinox, because there had just been three
intercalations at short, two-year intervals; this was corrected by making only
one intercalation between 552 and 546, bringing back the beginning of
Nisannu (in 546) to just before the equinox. But short-term,ad hocmeasures
of this kind did not prevent the overall tendency towards over-intercalation.
Thefine tuning needed for maintaining consistent synchronism with the
seasonal year would have required a long-term policy of intercalation which
was simply not in existence.^105
Intercalation in the early Achaemenid periodAt the beginning of the Achaemenid period, wefind a long interval of 3½ years
(from 541/0 to 537/6) followed by an obviously corrective, short interval of 1½
years (from 537/6 to 536/5) (seeTable 2.2). These irregularities were clearly
related to Cyrus’conquest of Babylon and overthrow of the neo-Babylonian
dynasty (in 539), as a result of which intercalation would have been put on
hold and only resumed in Cyrus’s second year (537/6).^106 This excessive delay
indicates, again, the extent to which Babylonian intercalation depended on the
king.
After this initial crisis, regular patterns of intercalation appear to have
becomefirmly established. From 536/5, a steady alternation of 3- and 2½-
year intervals was sustained throughout the reigns of Cyrus and Cambyses,
only to be discontinued soon after the accession of Darius (in 522). This must
be interpreted, again, as a politically led attempt tofix the intercalation. This
(^104) In Nebuchadnezzar’s reign there were 16 intercalations in about 42 years, thus an average
of 8 intercalations in 21 years. In Nabunaid’s reign (555–539), there were 6 intercalations in 16
years. From Nebuchadnezzar’s accession to the fall of the dynasty, there were altogether 24
intercalations in 65 years. All these exceed the optimal frequency of 7 intercalations in 19 years.
Consequently, Nisannu was occurring increasingly late in relation to the vernal equinox (Britton
1993: 66–8).
(^105) Britton (2007) 120–4 believes that over-intercalation in this period was part of a
grand, long-term calendrical policy; see discussion below, n. 126.
(^106) Similarly Britton (2007) 121, with another possible example of a delayed intercalation in
626 BCE, this one related to the formal accession of Nabopolassar in the following year.
102 Calendars in Antiquity