The writing of contemporary history was associated with the register of the magistrates. The register reaching farthest back, which was accessible to the later Roman inquirers and is still indirectly accessible to us, seems to have been derived from the archives of the temple of the Capitoline Jupiter; for it records the names of the annual presidents of the community onward from the consul Marcus Horatius, who consecrated that temple on the 13th Sept. in his year of office, and it also notices the vow which was made on occasion of a severe pestilence under the consuls Publius Servilius and Lucius Aebutius (according to the reckoning now current, 291), that thenceforward a nail should be driven every hundredth year into the wall of the Capitoline temple. Subsequently it was the state officials who were learned in measuring and in writing, or in other words, the pontifices, that kept an official record of the names of the annual chief magistrates, and thus combined an annual, with the earlier monthly, calendar. Both these calendars were afterwards comprehended under the name of Fasti - which strictly belonged only to the list of court-days. This arrangement was probably adopted not long after the abolition of the monarchy; for in fact an official record of the annual magistrates was of urgent practical necessity for the purpose of authenticating the order of succession of official documents. But, if there was an official register of the consuls so old, it probably perished in the Gallic conflagration (364); and the list of the pontifical college was subsequently completed from the Capitoline register which was not affected by that catastrophe, so far as this latter reached back. That the list of presidents which we now have - although in collateral matters, and especially in genealogical statements, it has been supplemented at pleasure from the family pedigrees of the nobility - is in substance based from the beginning on contemporary and credible records, admits of no doubt. But it reproduces the calendar years only imperfectly and approximately: for the consuls did not enter on office with the new year, or even on a definite day fixed once for all; on the contrary from various causes the day of entering on office was fluctuating, and the -interregna- that frequently occurred between two consulates were entirely omitted in the reckoning by official years. Accordingly, if the calendar years were to be reckoned by this list of consuls, it was necessary to note the days of entering on and of demitting office in the case of each pair, along with such -interregna- as occurred; and this too may have been early done. But besides this, the list of the annual magistrates was adjusted to the list of calendar years in such a way that a pair of magistrates were by accommodation assigned to each calendar year, and, where the list did not suffice, intercalary years were inserted, which are denoted in the later (Varronian) table by the figures 379, 383, 421, 430, 445, 453. From 291 u. c. (463 B. C.) the Roman list demonstrably coincides, not indeed in detail but yet on the whole, with the Roman calendar, and is thus chronologically certain, so far as the defectiveness of the calendar itself allows. The 47 years preceding that date cannot be checked, but must likewise be at least in the main correct[12]. Whatever lies beyond 245 remains, chronologically, in oblivion.
No era was formed for ordinary use; but in ritual matters they reckoned from the year of the consecration of the temple of the Capitoline Jupiter, from which the list of magistrates also started.