Sestertius

Sestertius, a Roman coin, was the fourth part of the Denarius (q.v.), and thus contained at first $2\backslash frac\{1\}\{2\}$ ases or libræ. The symbols for it were indifferently HS or IIS, the former being only a modification of the latter, which expresses two units and S for the additional half-unit (semis). In the Latin classics the phrase sestertius nummus, or merely nummus, is frequently employed to denote this coin. When the denarius was made to contain 16 ases the relation between it and the sestertius was preserved, and the latter from that time contained 4 ases. Till the time of Augustus, when the relation of the denarius to the ases was changed, the sestertius was worth fully 2d., but after this about an eighth less. Sestertium (before Augustus = £8, 15s. sterling) came to be used as if a neuter singular for 1000 sesterces; but with a numeral adverb attached, as decies sertertium, was used to signify 100,000 sesterces. It was the 'money of account' (never a 'coin') used in the reckoning of large sums. HSX = decem millia sestertium; HS|X = decies sestertium.