calendar followed from the outset the structure of true Julian calendar, with
leap years every four years.^84 This pushes the date of the institution of the
calendar to later in the 20sBCE.Within this consensus, Chris Bennett (2003)
(2007) has proposed a model of the Alexandrian and Roman calendars
that reconciles all the documentary evidence, and that should therefore be
preferred—at least on the basis of the evidence that is currently extant.
According to this model, the Alexandrian calendar began, in practical terms,
in 22BCEwhen thefirst leap year was observed (see Table 5.4).^85
This model entails that the institution of the Alexandrian calendar did not
immediately follow the annexation of Egypt in 30BCE, and that the three leap
years that were made in the Roman calendar in 29, 26, and 23BCEhad no effect
or influence on the Egyptian calendar. The limited influence of the Roman
calendar is evident, furthermore, in that the Alexandrian calendar was insti-
tuted with leap years every four years, whereas the Romans in this period were
making them every three. This suggests that the institutors of the Alexandrian
calendar had no intention, at least at the time, of conforming to the Roman
calendar and stabilizing their calendar in relation to the latter. This point,
often overlooked, is surprising and demands an explanation, because it ap-
pears to defeat the whole purpose of the Egyptian calendar reform.
It seems fairly clear that the institutors of the Alexandrian calendar were
driven, infirst instance, by a concern for scientific accuracy. As has been noted
in Chapter 3, for some centuries already the Egyptians had known that
conformity of the civil calendar to the solar year would require the intercala-
tion of one day every four years: this principle was stated (though not
successfully implemented) in the decree of Canopus of 238BCE.^86 In Chapter
4 we have seen that Julius Caesar drew on Alexandrian tradition and expertise
for the design of his new calendar, and that his original intention had almost
certainly been to insert a leap year every four years—even though, in practice,
his successors misunderstood this and inserted it every three. It was thus
probably known in Egypt that the Roman three-year interval was a mistake.
The decision to institute a leap year every four years in the Alexandrian
calendar was probably intended as a correction of the Roman mistake and a
(^84) Hagedorn (1994), A. Jones (2000b), Bennett (2003), (2004a). Most important is the
evidence of pap. Vindob. L. 1c and P. Oxyrhynchus LXI 4175 (an astronomical source relating
to the year 24BCEwith Egyptian and Roman datings, on which see mainly Jones, loc. cit.).
(^85) In earlier publications, Bennett (2003), (2004a: 168) inferred from SB 18. 13849 that the
first Alexandrian leap year was possibly in 24BCE, which would entail an interruption of the four-
year cycle of leap years between 12 and 6BCEwith a six-year interval instead (which is historically
difficult to explain). But this inference has been convincingly refuted by Bennett (2007); thefirst
Alexandrian leap year was therefore in 22BCE, and the four-year cycle was followed thereafter
without interruption
(^86) Hannah (2005) 113 notes that the average year length of 365¼days might also have been
known already as the foundation of Callippus’cycle, which was designed in Athens in the 4th c.
BCE(Geminus,Elem. Astr.8. 50–60: see Ch. 1 n. 89).
Fragmentation: Babylonian and Julian Calendars 265