ROMAN REPUBLICAN: C. Calpurnius Piso L.f. Frugi, 67 or 61 BC, AR Denarius (18mm, 3.97g, 5h). Rome Mint, 67 BC. Obverse: Head of Apollo right, wearing taenia; symbol for 10,000 behind. Reverse: C•PISO•L•F•FRVG; rider on horse galloping right, reins in right hand, palm in left, two pellets above, pellet below. Crawford 408/1b, symbols 103/123.
10,000 is the large number behind the head of Apollo. "The modern Roman numerals D for 500 and M for 1000 were not used in ancient times; D is in fact a misreading of the Roman I? and the Romans wrote 1000 as CI?, again misinterpreted as M. 10000 was written CCI?? but the "Cs" on both side could be nested inside each other. 100000 was written CCCI??? (often nested) and its half 50000, split vertically, as CCCI; 100000 is quartered by splitting both vertically and horizontally, and nesting the "Cs", resulting in the numeral 25000. Hersh in his manuscript on symbols on Roman Republican coins describes this variety among coins that have a number on the obverse and a fractional number on the reverse. The single dot above and below on reverse are also numbers, in this case fractions, a single dot being 1/12 or an unciae." So the whole coin adds up to 10000.167. - Andrew McCabe.