Sesterius, a silver coin, in use among the ancient Romans, called also simply nummus, and sometimes nummus sesterius. The sesterius was the fourth part of the denarius, and originally contained two asces and a half. It was at first denoted by LLS; the two L's signifying two librae, and the S half. But the librarii, afterwards converting the two L's into an H, expressed the sesterius by HS. The word sesterius was first introduced by way of abbreviation for semiliberius, which signifies two, and a half of a third, or literally, only half a third; for in expressing half a third, it was understood that there were two before.

Some authors make two kinds of sesterces; the less called sesterce, in the masculine gender; and the great one, called sesterium, in the neuter: the first, that we have already described; the latter containing a thousand of the other. Others will have any such distinction of great and little sesterces unknown to the Romans: sesterius, say they, was an adjective, and signified as sesterce, or two asces and a half; and when used in the plural, as in quinquaginta sesterceum, or sestercia, it was only by way of abbreviation, and there was always understood centena, millia, &c.

This matter has been accurately stated by Mr Raper, in the following manner. The substantive to which sesterius referred is either as, or pondus; and sesterius as is two asces and a half; sesterium pondus, two pondus and a half, or two hundred and fifty denarii. When the denarius passed for ten asces, the sesterius of two asces and a half was a quarter of it; and the Romans continued to keep their accounts in these sesterces long after the denarius passed for fifteen asces; till, growing rich, they found it more convenient to reckon by quarters of the denarius, which they called nummi, and used the words nummus and sesterius indifferently, as synonymous terms, and sometimes both together, as sesterius nummus; in which case the word sesterius, having lost its original signification, was used as a substantive; for sesterius nummus was not two nummi and a half, but a single nummus of four asces. They called any sum under two thousand sesterces so many sesterii in the masculine gender; two thousand sesterces they called dua or bina sesteria, in the neuter; so many quarters making five hundred denarii, which was twice the sesterium; and they said dina, vicena, &c. sesteria, till the sum amounted to a thousand sesterces, which was a million of sesterces. But, to avoid ambiguity, they did not use the neuter sesterrium in the singular number, when the whole sum amounted to no more than a thousand sesterces, or one sesterium. They called a million of sesterces decies nummum, or decies sesterium, for decies centena millia nummorum, or sesteriarum (in the masculine gender), omitting centena millia for the sake of brevity. They likewise called the same sum decies sesterium (in the neuter gender) for decies centes sesterium, omitting centes for the same reason; or simply decies, omitting centena millia sesterium, or centes sesterium; and with the numeral adverbs deces, vicie, centier, millier, and the like, either centena millia or centes was always understood. There were their most usual forms of expression; though for bina, dina, vicena sesteria, they frequently laid bina, dina, vicena millia nummum. If the conular denarius contained 60 troy grains of fine silver, it was worth somewhat more than eight-pence farthing and a half sterling; and the as, of 16 to the denarius, a little more than a half-penny. To reduce the ancient sesterces of two asces and a half, when the denarius passed for 16, to pounds sterling, multiply the given number by 5454, and cut off six figures on the right hand for decimals. To reduce nummi sesterii, or quarters of the denarius, to pounds sterling; if the given sum be conular money, multiply it by 8727, and cut off six figures on the right hand for decimals; but for imperial money diminish the said product by one-eighth of itself. Phil. Trans. vol. lxi. part ii. art. 48.

To be qualified for a Roman knight, an estate of 400,000 sesterces was required; and for a senator, of 800,000.

Authors also mention a copper sesterce, worth about one-third of a penny English.

or sesterius, was also used by the ancients for a thing containing two wholes and an half of another, as \( ax \) was taken for any whole or integer.