A. E. Samuel, Greek and Roman Chronology, 163, notes that Appian, De Bello Punica 99, records that sickness fell on the camp beseiging Carthage at the time of the heliacal rising of Sirius (i.e. 27 July), and that the consul Censorinus left soon thereafter to conduct elections for the next year. Since elections at this time were normally held around November, this suggests he left in late September or early October to arrive in Rome no later than mid October; hence 27 July should fall in mid September.
However, Brind'Amour, Le calendrier romain, 128, objects that Appian lists a number of other events between the sickness and Censorinus' departure, hence that mid September could be some time later. This is a valid point, but what it means is that Samuel's argument establishes a terminus post quem rather than a synchronism; perhaps it allows 27 July to fall a few weeks earlier than mid September on the Roman calendar. Hence the synchronism allows us to estimate the minimum number of intercalations between A.U.C. 586 = 168 and Id. Sept. A.U.C. 605 = c. 27 July 149.
On this basis, the relationship between the Julian date of Id. Sept. A.U.C. 605 and the minimum number of intercalations between A.U.C. 586 and A.U.C. 605 is as follows:
Number of Intercalations Number of intercalated days Julian date of Id. Sept. A.U.C. 605
A.U.C. 586-6059 198-207 5-13 July 149
10 220-230 27 July - 5 August 149
We may therefore estimate that intercalations occurred at a minimum average frequency of roughly one intercalation every alternate year in this period. However, they may also have occurred more often. On the reconstruction given here, 27 July 149 = a.d. XVII Kal. Sept. A.U.C. 605, and Id. Sept. A.U.C. 605 = 24 August 149, suggesting that Censorinus left camp about a month after the rising of Sirius.
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