Semissis

Moneta Historical Research by Tom Schroer

The Semissis was a gold weighing 2.25 g. coin introduced by Constantine, and was worth 1/2 of a solidus. It was replaced by the tremissis (1/3 solidus) in the reign of Theodosius I.

"Semissis" is the genitive form of the Latin noun "semis", which means "a half". The term can properly be applied to both an early Roman bronze coin and the late Roman half of the golden solidus. However, modern practice is to use the term "semis" for the bronze half-as coin, and the term "semissis" is normally confined to the late Roman gold coin.

The solidus (Latin for "trustworthy") was a golden coin introduced by Constantine I at the end of 309 or beginning of 310. It replaced the "aureus", which had been of extremely variable weight in the third century. The solidus was not adopted by the Tetrarchy, and it was only after Constantine's final victory over Licinius I in 324 in the Second Civil War that the solidus (as well as Constantine!) reigned supreme.

Gold fractions of the solidus appeared at the Treveri mint simultaneously with the introduction of the solidus, but from their weight they appear to have been 3/8 of a solidus, or "1½ scripulum" pieces. The first true halves were did not make their appearance until 320 at Sirmium, and continued to be even more scarce than the "1½ scripulum" pieces throughout the reign of Constantine and his sons. The theoretical weight of the semissis was 1/144 of the Roman pound, or about 2.27 grams, which corresponds very closely to its actual struck weight. Since the solidus, of which it was a fraction, was very stable in weight over the centuries, the semissis varied little from its original 2.27 gram weight. In Roman times the semissis, like all Roman gold, was usually in excess of 98% fine.

Gold fractions were never very common until about the fifth century, and even then the tremissis, or 1/3 solidus (which had replaced the 1½ scripulum piece after about 385), was much more common than the semissis. The semissis continued to be struck until well into Byzantine times (the last known are of the reign of Basil I (867-886)), although again it never played a principal part in the monetary system.