« A.U.C. 691 = 63 B.C. »

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 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.

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.

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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