AERARIUM, in ancient Rome the public treasury. The treasury contained the moneys and accounts of the State, the standards of the legions, the public laws, the decrees of the senate, etc. These were deposited in the temple of Saturn and, during the republic, were in charge of the urban quaestors (see QUAESTOR), under the control of the senate. In 28 B.C. Augustus transferred the aerarium to two praefecti aerarii; in 23 B.C. these were replaced by two praetors (praetores aerarii or ad aerarium), selected by lot during their term of office. In addition to the common treasury, there was a special reserve fund, also in the temple of Saturn, the aerarium sanctum (or sanctius), originally consisting of the spoils of war, afterwards maintained chiefly by a 5% tax on the value of all manumitted slaves.
This fund was not to be touched except in cases of extreme necessity. Under the emperors the senate continued to have the nominal management of the aerarium, while the emperor had a separate exchequer, called fiscus, filled largely with the profits from the imperial domains in Egypt and elsewhere. But after a time, as the power of the emperors increased, this distinction virtually ceased. Besides creating the fiscus, Augustus also estab lished in A.D. 6 a military treasury (aerarium military), endowed by the emperor himself (see Monumentum Ancyranum, iii. 35) and supported by the proceeds of the tax on public sales and the succession duty. Its administration was in the hands of three praefecti aerarii militaris, senators of praetorian rank.
The tribuni aerarii have been the subject of much discussion. By the lex Aurelia (7o B.c.) the list of iudices (jurymen) was composed, in addition to senators and equites, of tribuni aerarii. Whether these were the successors of the tribuni aerarii who in earlier times were paymasters of the troops, etc., or a new order closely connected with the equites, is uncertain. According to Mommsen, they were persons who possessed the equestrian census, but no public horse. They were removed from the list of iudices by Caesar, but replaced by Augustus. According to Madvig, the original tribuni aerarii were not officials but private individuals of considerable means, who undertook certain financial work connected with their own tribes. The term was subse quently extended to include all those who possessed the property qualification that would have entitled them to serve as tribuni aerarii.
Tacitus, Annals, xiii. 29, with Furneaux's notes; J. E. Sandys, Companion to Latin Studies (1921), useful bibliography. On the tribuni aerarii, see A. H. J. Greenidge, Legal Procedure (Igo') ; W. E. Heitland, The Roman Republic, §957 (1923).