"ubi Servius: Annus dictus quasi Anus, id est Anulus; quod in se redeat, &c."
That the Roman word Æra signified number in earlier times, we learn from Nonius Marcellus:
"Æra numeri nota, Lucilius lib. xxviiij. Hoc est ratio perversa, æra summa, et subducta improbe."
Those who desire further confirmation will find it in that extraordinary storehouse of erudition, the Exercitationes Pliniana of Salmasius, p. 483., ed. 1689.
It is equally certain that, soon after the establishment of the Gothic domination in Spain, it was applied in its present signification; but that it also signified time or period will be evident from the following passage of the Coronica General, Zamora, 1541. fol. CCC.XXVJ. Speaking of the numbers of the extraordinary armament assembled by Don Alonzo, preparatory to the battle of Las Navas:
"E para todo esto complir avia menester el rey Don Alfonso de cada dia doze mil maravedis de aquella ERA, que era buena moneda."
That is to say, money of that time.
From our imperfect acquaintance with the early history of the Goths, it is not easy to decide upon the reasons why they adopted their mode of reckoning from thirty-eight years before the Christian epoch; but if we accept the signification which we know it was not unusual to affix to the word Era, namely, that of year, time, or period, the solution is easy as to its origin. It was only the engrafting of their own vernacular word into the barbarous Latin of the time, from whence also it was adopted into the Romance, Castilian, or Spanish.
It may also be observed that Liutprand uses the word in this sense: in speaking of the Mosque of San Sophia at Constantinople, and how the course of the reign of its rulers was noted there, so as to be manifest to all, he concludes:
"Sic ÆRAM qui non viderunt intelligunt."