actually known to the druids, scholars have grossly exaggerated the amount of
astronomical knowledge that would have been needed for the creation of the
Coligny calendar—whether as afive-year cycle, or even as the complex 25-year
scheme that Olmsted has proposed. In actual fact, only minimal astronomical
knowledge would have been necessary to construct this calendar. Its basic
structure, as we have seen, consists of a simple alternation of 29- and 30-day
nights, with possibly a few variations to the month of Equos that show signs of
trial and error (see above, near n. 16) and that do little to improve the
calendar’s lunar accuracy. Intercalation at 2½-year intervals is also a rather
elementary and inaccurate scheme;^32 even the omission of an intercalary
month every 25 years, which somewhat rectifies this inaccuracy, could have
been determined empirically without much astronomical expertise. It is true
that dates of solstices, assuming Olmsted’s interpretation of the three-letter
notations, could not have been determined astronomically without consider-
able expertise; but scholars have failed to note that in the Roman period, the
Julian calendar would have provided a convenient and reliable way of com-
puting solstices and equinoxes over lengthy periods without any astronomical
expertise whatsoever (only arithmetical competence would have been neces-
sary). Nothing compels us to assume, therefore, that the 25-year scheme that
may be implicit in the Coligny calendar was the result of centuries of druidic
astronomical inquiry. It could just as well have been conceived from scratch in
the second centuryCE, when the Julian calendar would have provided an easy
way of computing its more complex features.^33
(^32) As we have seen in Ch. 2, this scheme was adopted in Babylon during Nabopolassar’s reign
(625– 604 BCE) but abandoned immediately thereafter, and later succeeded by the more accurate
19-year cycle.
(^33) The late-2nd–early-3rd-c. clepsydra reportedly discovered in Germany in the river Rhine,
which comprises aparapegmaof the Julian calendar with conventional Julian dates of solstices
and equinoxes (e.g.a.d. VIIIkal. Iul.for the summer solstice: see Ch. 5 n. 162), provides clear
evidence that knowledge of these dates would have been available in the region in approximately
the same period (AE2003: 1279). The sequence of TII marks does not match exactly the
sequence of solstices of the Julian calendar, because it is based on afive-year (or 25-year)
cycle, whereas Julian leap years follow a four-year cycle; but this prevent the Julian calendar
from having been used as the basis for determining and calculating the solstices of the Coligny
calendar. Olmsted (1992) 126–30 shows that the TII scheme lags behind the solar year by one
day in 454 years, whereas the Julian calendar exceeds the solar year by one day in 128 years; he
credits the druids for discovering and designing a more accurate scheme‘which theWestern
world was to await 1700 years to rediscover’(ibid. 128). I would submit, however, that the greater
solar accuracy of the TII scheme was not deliberate, nor based on independent astronomical
knowledge, but rather only the fortuitous result of adapting conventional Julian solar dates to a
lunar 25-year cycle. It should also be noted that although the authors of the TII scheme were
surely aware of its slight divergences from the solstice dates of the Julian calendar, we have no
evidence that they knew or considered their scheme to be more accurate than the Julian (see
above, n. 25).
310 Calendars in Antiquity