Roman Semis: History of the Ancient Bronze Half-As Coin

Illustrated Specimen Details: Bronze Semis

Example Specimen: Semis, 154-133 BC (City of Castulo, Hispania)

Authority & Design: This bronze semis was minted in the ancient Iberian town of Castulo (Iberian "Kastilo") during a period when the Roman monetary system was spreading across the Iberian Peninsula, following the city's alignment with the Roman Republic during the Second Punic War (218-201 BC). The obverse features the portrait of a young man, often identified by numismatists as Apollo, accompanied by the partial inscription KASTILO. The reverse displays a prominent bull with a crescent above it. While the inscriptions on this specific specimen are largely lost to time, standard varieties of this type typically contain the legend CN FVL CNF - CN VOC ST F. Despite detailed analyses, the exact historical meaning of these specific abbreviations remains debated among experts.

1. ANCIENT ROME (3rd century BC - 2nd century AD) — ROMAN REPUBLIC + ROMAN EMPIRE + ROMAN PROVINCES + DEPENDENT TERRITORIES (Iberia, Numidia...): 1 semis = 2 quadrans = 1/2 as

The name of the semis coin translates directly from Latin as "half", representing its nominal value as exactly half of an as. Interestingly, the ancient Romans also used the term "semis" as a standard unit of measurement in mathematics for weight, length, and area to denote a half fraction of any corresponding basic unit.

History and Evolution of the Semis

The semis was an essential fractional bronze coin of the ancient Roman monetary system. Introduced during the early Roman Republic around the 3rd century BC, the denomination circulated extensively for centuries before finally ceasing production by the time of Emperor Hadrian in the 2nd century AD.

The standard Roman base-12 value system was structured as follows:

• 1 as = 2 semisses

• 1 semis = 1/2 as (equivalent to 6 unciae)

From Heavy Cast Bronze to Provincial Struck Coins

In its earliest Republican form, the semis was an enormously heavy cast bronze coin, with initial specimens weighing between 70-90 grams. Over centuries of inflation and monetary reform, the coin transitioned to a struck manufacturing method and was significantly reduced in size, eventually weighing around 4 grams during the later Republican period. Early types are easily identifiable by a symbolic denomination mark — either the Roman letter "S" or six dots (••••••) indicating six unciae. They frequently featured the head of Saturn on the obverse and the prow of a warship on the reverse.

As Rome expanded its geopolitical dominance, its monetary system followed. The semis became a crucial everyday coin for small market transactions not only in the Italian peninsula (including pre-republican Etruria) but across the Carthaginian Empire and various Roman provinces. In regions like ancient Iberia, local peoples such as the Celtiberians minted their own regional variations under Roman authority. The Castulo semis is a perfect example, blending Roman economic standards with local cultural imagery, such as the prominent bull and crescent.

Numismatic Perspective

For modern collectors, the semis offers a fascinating cross-section of ancient Mediterranean history. Because it was issued across the Republic, the Empire, and dependent territories, the denomination provides incredible variety. While Imperial semisses often lack distinctive features compared to other fractional bronzes below the denarius, the Republican and provincial issues — with their unique mint marks, local deities, and varying weight standards — serve as vital historical documents of daily commercial life in the ancient world.