William Smith, D.C.L., LL.D.:
A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.

SESTE′RTIUS, a Roman coin, which properly belonged to the silver coinage, in which it was one-fourth of the denarius, and therefore equal to 2½ asses. Hence the name, which is an abbreviation of semis tertius (sc. nummus), the Roman mode of expressing 2½ (Varro, L. L. V.173, ed. Müller; Festus, s.v.; Plin. H. N. XXXIII.3 s13). The word Nummus is often expressed with sestertius, and often it stands alone, meaning sestertius.

Hence the symbol H S or I I S, which is used to designate the sestertius. It stands either for L L S (Libra Libra et Semis), or for I I S, the two I's merely forming the numeral two (sc. asses or librae), and the whole being in either case equivalent to dupondius et semis (Priscian, de Ponder. p1347; Festus, p347, Müller).

When the as was reduced to half an ounce, and the number of asses in the denarius was made sixteen instead of ten [As, Denarius], the sestertius was still ¼ of the denarius, and therefore contained no longer 2½, but 4 asses. The old reckoning of 10 asses to the denarius was kept, however, in paying the troops (Plin. H. N. XXXIII.3 s13). After this change the sestertius was coined in brass as well as in silver; the metal used for it was that called Orichalcum, which was much finer than the common Aes, of which the asses were made (Plin. H. N. XXXIV.2).

The sum of 1000 sestertii was called sestertium. This was also denoted by the symbol H S, the obvious explanation of which is "I I S (2½) millia;" but Gronovius understands it as 2½ pounds of silver (sestertium pondus argenti), which he considers to have been worth originally 1000 sestertii, and therefore to have represented this value ever after (Pec. Vet. I.4, 11). The sestertium was always a sum of money, never a coin; the coin used in the payment of large sums was the denarius.

According to the value we have assigned to the Denarius, up to the time of Augustus, we have

after the reign of Augustus

Taking the earlier value of the sestertius, and neglecting the half farthing, we have 1 sestertius = two-pence, 6 sestertii = 1 shilling, and 120 sestertii = 1l. sterling. Hence we get the following very convenient Rule: to convert sestertii into  p1043 pounds divide by 120; and correct the result by adding to it the quotient obtained by dividing the original number by 1920: for ·5 of a farthing is always 1⁄1920 of a pound.

The sestertius was the denomination of money almost always used in reckoning considerable amounts. There are a very few examples of the use of the denarius for this purpose. The mode of reckoning was as follows:—

Sums below 1000 sestertii were expressed by the numeral adjective joined with either of these forms.

The sum of 1000 sestertii = mille sestertii = M sestertium (for sestertiorum) = M nummi = M nummum (for nummorum) = M sestertium nummum = sestertium. These forms are used with the numeral adjectives below 1000, for sums between 1000 and 1,000,000 sestertii: sometimes millia is used instead of sestertia: sometimes both words are omitted: sometimes nummum or sestertium is added. For example, 600,000 sestertii = sescenta sestertia = sescenta millia = sescenta = sescenta sestertia nummum.

For sums of a thousand sestertia (i.e. a million sestertii) and upwards, the numeral adverbs in ies (decies, undecies, vicies, &c.) are used, with which the words centena millia (a hundred thousand) must be understood. With these adverbs the neuter singular sestertium is joined in the case required by the construction (Nepos, Att. xiv.2, gives sestertio vicies and sestertio centies). Thus, decies sestertium = decies centena millia sestertium = ten times a hundred thousand sestertii – 1,000,000 sestertii = 1000 sestertia: millies H S = millies centena millia sestertium = a thousand times one hundred thousand sestertii = 100,000,000 sestertii = 100,000 sestertia. When an amount is described by more than one of these adverbs in ies, they must be added together if the larger number stands first, but multiplied when the smaller is first; care however being taken not to reckon the centena millia which is understood, more than once in the whole amount. Thus, Suetonius (Octav. 101) has millies et quingenties for 150,000 sestertia, i.e. 100,000,000 + 50,000,000 = 150,000,000 sestertii, and immediately after quaterdecies millies for 1,400,000 sestertia, i.e. 14 × 1000 + 100,000 (= 1,400,000,000) sestertii. A variety was allowed in these forms: thus Cicero uses decies et octingenta millia for 1800 sestertia, i.e. 1,000,000 + 800,000 sestertii, and quaterdecies for 1400 sestertia, i.e. 14 × 100 sestertia, i.e. 14 × 100,000 sestertii (In Ver. I.39).

When the numbers are written in cypher, it is often difficult to know whether sestertii or sestertia are meant. A distinction is sometimes made by a line placed over the numeral when sestertia are intended, or in other words, when the numeral is an adverb in ies. Thus:—

HS. M. C. = 1100 sestertii, but

HS. M. C. = HS millies centies = 110,000 sestertia = 110,000,000 sestertii.

Wurm (p24) gives the following rule: When the numbers are divided into three classes by points, the right-hand division indicates units, the second thousands, the third hundreds of thousands. Thus, III.XII.DC = 300,000 + 12,000 + 600 = 312,600 sestertii. But these distinctions are by no means strictly observed in the manuscripts.

Like other parts and multiples of the as, the sestertius is applied to other kinds of magnitude, e.g. pes sestertius for 2½ feet.

It has been assumed throughout this article that the forms of sestertium, as a neuter singular, are genuine, a fact which may admit of doubt.

Sesterce is sometimes used as an English word. If so, it ought to be used only as the translation of sestertius, never of sestertium.

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