Aera, Was also a citie of Macedonia, an other of Ionia, and also of Hellespont.
Lewis and Short: Latin dictionary
aera, ae, f. [from aera, counters; v. aes, 2. E., later Lat. I. In math., a given number, according to which a reckoning or calculation is to be made, Vitruvius (Vetrubius) Rufus ap. Salmas. Exercc. I. p. 483.— II.Anitem of an account (for the class. aera, plur. of aes, Ruf. Fest. in Breviar. init. The passage of Lucil. cited by Non. 2, 42, aera perversa, is also prob. plur.).—III.An era or epoch from which time is reckoned, Isid. Orig. 5, 36; cf. Inscr. Orell. II. p. 374.