Augustus was born on a.d. IX Kal. Oct. of A.U.C. 691 = 63 (Suetonius, Augustus 5). A number of accounts of his horoscope survive, which give his astrological birth sign as Capricorn (e.g. Suetonius, Augustus 94.12). Capricorn is also given in coinage. There are also some indications that he was born under Libra (e.g. Manilius 4.773-777, not explicit but in a work dedicated to Augustus); however, the dominant evidence refers to Capricorn.
There are several schools of thought on the significance of this synchronism. As surveyed in T. S. Barton, JRS 85 (1995) 33, they are: that Libra is his solar birth sign but he was conceived under Capricorn (Scaliger, Bouché-Leclercq and others in various guises); that the moon was in Capricorn at the time of his birth (Housman); or that Capricorn is his (lunar) birth sign and the references to Libra actually apply to the lunar sign of Tiberius (Bickel, Voigt) -- it being argued that Augustus has died by Manilius 4. In 63, the sun was ascendant in Libra from 17 September to 17 October, and in Capricorn from 15 December to 14 January.
Many authors, from Kepler to Brind'Amour, have spent a great deal of effort in analysing the various literary texts to understand the significance of these alignments, but for chronological purposes we need to focus on the calendrical aspects of the problem rather than the literary ones. Given that Kal. Mart. A.U.C. 696 = 24 February 58, and assuming no intercalations between A.U.C. 691 = 63 and A.U.C. 695 = 59, a.d. IX Kal. Oct. A.U.C. 691 fell on either 12 or 13 October 63; assuming one intercalation, it fell on 18, 19 or 20 September 63. Any more intercalations will force the birth of Augustus back into Virgo or earlier, but there is insufficient time to allow the number of intercalations necessary to force the birth of Augustus back into Capricorn of the previous year. Alternately, in order to move his birth forwards into Capricorn in 63 it would be necessary to remove at least 65 days of agreed intercalations, i.e. there would have to be only 1 intercalation between 63 and 46. Hence, if we accept that Libra was indeed Augustus' solar sign, it follows that there was zero or one intercalary month between A.U.C. 691 = 63 and A.U.C. 696 = 58.
The following considerations require that there was 1:
The next known intercalary year is A.U.C. 696 = 58. There is no other example of a run of four or more consecutive regular years since A.U.C. 564 = 190 until the gap between A.U.C. 702 = 52 and A.U.C. 708 = 46, and no indication in the sources that such an unusual event occurred.
- The evidence considered under A.U.C. 687 = 67 shows that there were 3 intercalations, either 3 of 23 days or 2 of 23 and 1 of 22 days, in the next decade, one of which was A.U.C. 696 = 58.
- The reconstructed Lex Acilia proposed here requires either one or two intercalations between A.U.C. 691 = 63 and A.U.C. 696 = 58.
The year of this intercalation is not known. However, in view of the analysis of A.U.C. 687 = 67, Kal. Mart. A.U.C. 691 = 1 or 2 March 63. We may conclude that Augustus was born on a.d. IX Kal. Oct. of A.U.C. 691 = 18 or 19 September 63.
There is, however, a complication. It remains necessary to explain the significance of Capricorn, and the most natural explanation is that it was his lunar sign. But at this time the moon was in Sagittarius, not Capricorn. We can place the moon in Capricorn by supposing that the astrologer was simply translating pre-Julian dates to the Julian calendar rather than converting them, i.e. simply equating a.d. IX Kal. Oct. A.U.C. 691 to 22 September 63. On this basis, the moon was indeed in Capricorn. (Similarly, Tiberius was born on a.d. XVI Kal. Dec. AUC 712 = 15 November 42 (Suetonius, Tiberius 5). At that time the moon was in Virgo. But if the date is simply translated to the Julian calendar, i.e. to 16 November, the moon was indeed in Libra.)
A.-M. Lewis, Phoenix 42 308 at 310 n. 8, having cited this page, dismisses the above date (18 or 19 September) on the grounds that "Bennett is unable to connect Capricorn with Augustus' horoscope". Either she did not read or she did not understand the previous paragraph.
There is a fundamental flaw in her reasoning: she supposes that the Julian date for which the horoscope was cast must represent the historical Julian date of Augustus' birth. It is quite clear from her paper that she has made no attempt to understand the complexities of pre-Julian chronology, she simply accepts Brind'Amour's result, that the two were equivalent in September of this year, as a given. Yet, if the early Julian reconstruction proposed here is correct, it is not possible for the Julian date of Augustus' birth to correspond to the Julian date of the horoscope, however correct her reconstruction of that horoscope may be.
The process suggested here is perfectly plausible. According to Suetonius (Augustus, 94.5), Augustus' horoscope was cast at his birth by Nigidius Figulus and recast by Theogenes in 44 (Augustus, 94.12). The first horoscope is clearly legendary. At the time of the second, according to the reconstruction proposed here the Roman calendar was only one day out of alignment with Julian, i.e. a.d. IX Kal. Oct A.U.C. 709 = 22 September 44, which is the date required for the desired alignment with Capricorn in A.U.C. 691 = 63.
However, this process suggests that Augustan-era astrologers did not actually perform accurate retrocalculations to determine Julian equivalents of pre-Julian dates of birth, but rather translated the pre-Julian dates to their Julian equivalents, as though the pre-Julian years were actually aligned to the Julian calendar. Had they done so, Augustus' solar sign would remain in Libra. This means that the horoscope data cannot be relied on to provide accurate historical dates. Nevertheless, since the pre-Julian year was in general approximately aligned to the Julian, this imprecision should still be good enough for approximate alignments. We may therefore accept that Augustus was in fact born under Libra or very close to it.
A-M. Lewis, Phoenix 42 308 at 315-321 presents a very plausible case that the deified Caesar of Virgil's Georgics 1.32-35, who is there associated with Libra, is Julius Caesar, not Augustus. However, one of her arguments (p318) is, that at the time of Caesar's birthdate, a.d. III Id. Quint. AUC 654, "there is no overwhelming evidence that the Roman calendar was seriously out of step with the seasons in that year", and that the Julian transliteration, July 13 100 BC, is a date when the moon was in Libra. This argument is very doubtful.
If Virgil, writing in 42 BC, had considered Id. Quint. AUC 654 as though it were a Julian date, he would have placed the moon in Libra at that time. However, it is not true that this result follows from the agreed fact that "there is no overwhelming evidence that the Roman calendar was seriously out of step with the seasons in that year". The moon was only in Libra from 3 days in the month, so the Roman and Julian calendars would have to have been in near-perfect alignment for Lewis' date to be historically accurate. While the alignment is not absolutely certain, on the reconstruction proposed here a.d. III Id. Quint. AUC 654 = 19 June 100, at which time the moon was in Sagittarius.
Thus, Lewis' argument provides additional evidence for the theory proposed here: that horoscopes cast in early Julian times treated pre-Julian dates as though they were Julian dates and therefore have no historical value for determining the alignment of the calendar.
A. W. Lintott, CQ 18 (1968) 189, 190 n. 10, notes that Cicero, De divin. I.17, extolling the celestial phenomena that attended his consulate in A.U.C. 691 = 63, describes Jupiter as "filling the whole sky". He argues that this refers to the opposition of Jupiter on 3/4 Dec 64, at which time it reached its maximum brightness, and concludes that Cicero's consulate must have started earlier. This result is only possible if this year is intercalary. Brind'Amour, Le calendrier romain 58, disputes this analysis, arguing (inter alia) that the passage refers to Jupiter the deity, not to the planet.
With no other reason to regard A.U.C. 691 = 63 as intercalary, and since he believes A.U.C. 692 = 62 is intercalary, he assigns this year as a regular year to avoid consecutive intercalations. He is left with either A.U.C. 690 = 64 or A.U.C. 689 = 65 as a 377-day intercalary year. In his tables he opts, arbitrarily, for A.U.C. 689 = 65. However, he should have selected A.U.C. 690 = 64. Cicero Ad Atticum 1.1.1 records that an electoral concilium was held on a.d. XVI Kal. Sex. A.U.C. 689 = 65. This day is a nundinal B. Brind'Amour's model predicts the nundinal letter for the start of A.U.C. 689 = 65 was H, regardless of which of the two years were intercalary. If there were a 22-day intercalation, market days would fall on B days thereafter for the remainder of the year, which would prevent the holding of the concilium recorded by Cicero. Therefore, on Brind'Amour's model, A.U.C. 689 = 65 cannot have a 22-day intercalation.
The length of this year cannot yet be determined directly. On the reconstructed Lex Acilia proposed here, it was a regular year since there were only three intercalations between A.U.C. 687 = 67 and A.U.C. 697 = 57, including A.U.C. 696 = 58.
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