« A.U.C. 701 = 53 B.C. »
The length of this year is determined indirectly. Cicero Ad Atticum 4.3.4 tells us that a.d. X Kal. Dec. A.U.C. 697 = 57 was a market day. Hence the distance between this date and Kal. Ian. A.U.C. 702 = 52, another market day, was a multiple of 8 days. There are only two sets of year lengths under which this is possible: (i) two regular years of 355 days each and two of 378 days, and (ii) three regular years of 355 days each and one of 377 days.
It can be shown on independent grounds that A.U.C. 700 = 54 and A.U.C. 698 = 56 were both 355 days long. This leaves three possible distributions: (a) a 22 day intercalation in A.U.C. 699 = 55, or (b) in A.U.C. 701 = 53, or (c) 23 day intercalations in both A.U.C. 701 = 53 and A.U.C. 699 = 55. The choice is determined by elimination:
Cicero Ad Atticum 4.15.8 tells us that a.d. V Kal. Sex. A.U.C 700 was a comitial day, hence not a market day, but on option (b) this date is a multiple of 8 days from a.d. X Kal. Dec. A.U.C. 697. This excludes option (b).
- Cicero Ad Atticum 4.18.5 tells us that Caesar was on the point of leaving Britain on a.d. VI Kal. Oct. A.U.C. 700, while Caesar himself (De Bello Gallica 5.23) tells us he left Britain at the end of summer, shortly before the autumnal equinox. On option (a), Cicero's date is 29 August 54; on option (c) it is 6 August 54. This excludes option (c).
It follows that A.U.C. 699 = 55 was 377 days long and A.U.C. 701 = 53 was 355 days long. Since the Julian dates of A.U.C. 702 = 52 are known, this result fixes the Julian dates of each year between A.U.C. 698 = 56 and A.U.C. 701 = 53.
An approximate indication of the absolute dating of this year comes from Plutarch's account of the battle of Carrhae. Ovid, Fasti 6.465 gives its date as a.d. V Id. Iun. On Brind'Amour's reconstruction, this equates to 6 May 53; on mine to 4 May 53. The moon was in its first quarter at this time. According to Plutarch, Crassus 29.4, after Crassus' lieutenant Cassius failed in his attempt to escape from Carrhae on the second night following the battle, he was advised by his Arab guides to wait until the moon entered Scorpio. As noted by P. Brind'Amour, Le calendrier romain 42, the next time the moon entered Scorpio was on 11 and 12 May 53, and it was a full moon; these were in fact the only two nights of that year that the moon was full in Scorpio. Thus, the Arab advice was to wait a few days until the moon was full to get maximum night visibility for an escape.
This account is somewhat contradicted by Dio Cassius 40.25.3, who says that Crassus was not able to attempt to escape immediately from Carrhae because the moon was full, and that he had to wait till the new moon. This seems unlikely on the face of it, since it requires Crassus to stay put in Carrhae for up to two more weeks. Moreover, if the Arab advice was to wait until the moon was new in Scorpio, we are looking at dating the battle of Carrhae to November 53 or 54! This is not possible on any reconstruction. Thus, it appears that Dio misunderstood the Arab advice. Clearly, when the Roman survivors fled to the city of Carrhae on the night of the battle, there was enough moonlight to navigate by, and Dio presumably concluded that the escape attempts over the next few days failed due to too much light rather than too little. It appears that Plutarch's account is the more reliable.
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