first half of the month, between the Kalends and the Ides, there was no problem,
since there were no extra days inserted except at the end of the month; only if your
birthday fell between Ides and Kalends was there an issue. Augustus is not the only
observable case of a person in this situation who treated his or her birthday as
Caesar treated the festivals, keeping the same “day,” but changing the notation.
This could have highly bizarre results, as Suerbaum has finely demonstrated in the
case of M. Antonius.^110
Antonius was born in 83 b.c.e.on the day after the Ides of January (not that he
would have described the day in that way).^111 By the Republican calendar then in
operation, January is a short, 29-day, month, with the Ides falling on the thirteenth
day: according to our system, then, he was born on the fourteenth day of January.
To find the Roman date for this, since he is born after the Ides, Antonius must
count down (inclusively) to the next marker, the Kalends; since January has 29
days, his Republican birthday is “the seventeenth (inclusive) day before the
Kalends of February,” ante diem septimum decimum Kalendas Februarias.On 1
January 45 b.c.e., however, January acquires two extra days, to become a 31-day
month, so that Antonius faces a choice when he prepares to celebrate his thirty-
eighth birthday in that same month, his first birthday under the new Julian calen-
dar. Should he celebrate his birthday on the seventeenth day before the Kalends of
February, as he always had? In that case, however, he would be celebrating his
birthday two days later, on the third day after the Ides, not the day after the Ides.
What he did was to keep celebrating his birthday on the day after the Ides, and the
notation changes accordingly, in just the same way as we observed for the festival
of Apollo and the birthday of Augustus. The day after the Ides of January is no
longer seventeen (inclusive) days before the first day of February, but nineteen:
ante diem nonum decimum Kalendas Februarias.
This new Julian date, however, produces a bizarre result, for it is not a possible
date in the Republican calendar. When Antonius was born there was no such date
as “the nineteenth day before the Kalends of February,” since the farthest back you
can count from the next Kalends in a 29-day month before you bump into the Ides
is seventeen days: in the Republican calendar, nineteen days before the first day of
February is actually the day before the Ides of January. Antonius’s new Julian
birthday, then, is an anniversary of the dayhe was born in some sense, but it is not
actually the dateon which he was born, because when he was born this date could
not exist. This piquant but inconsequential result of the recalculation suddenly
acquired a potent weight of significance after Antonius’s death, when his memory
was damned. As commemorated on the Fasti Verulani, the Senate voted to mark
Calibrating across the Julian Reform. 155