The Semis denomination
The semis ('half') was a small Roman bronze coin that was valued at half an as. During the Roman Republic, the semis was distinguished by an 'S' (indicating semis) or 6 dots (indicating a theoretical weight of 6 uncia).

Some of the coins featured a bust of Saturn on the obverse, and the prow of a ship on the reverse.

Initially a cast coin, like the rest of Roman Republican bronzes, it began to be struck from dies shortly before the Second Punic War 218-204 BC.

The coin was issued infrequently during the Roman Empire, and ceased to be issued by the time of Hadrian 117-138 AD.
Semis
(1) Decius
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An AE Semis struck AD 249-250 in Rome
Obverse: IMP C M Q TRAIANVS DECIVS AVG, laureate, draped and cuirassed bust right

Reverse: Mars standing left, holding shield and spear; S C across field

Diameter: 18 mm
Die Orientation: 1 H
Weight: 2.39 g
No notes for this coin
RIC 128; Sear 9433
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An AE Semis struck 15 BC - 19 AD in Colonia Romula
Obverse: head left; GERMANICVS CAESAR TI AVG F

Reverse: shield within wreath; PERM AVG COL ROM

Diameter: 21 mm
Die Orientation: -
Weight: 6.5 g
No notes for this coin
RPC I 75
(3) Nero
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An AE Semis struck 65 A.D. in Lugdunum
Obverse: NERO CLAVD CAESAR AVG GERMA, bare head right, with globe at point of bust.

Reverse: CER QVINC ROM CON around, SC in exergue, Table, seen at an angle, surmounted by an urn on the left and wreath on the right.

Diameter: 21 mm
Die Orientation: -
Weight: 4.3 g
Scarce 60
RIC 488
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An AE Semis struck 12-14 AD in Lugdunum
Obverse: TI CAESAR AVGVST F IMPERAT VII, Head of Tiberius facing right, wearing laurel wreath

Reverse: Altar of Lugdunum, ROM ET AVG below

Diameter: 19 mm
Die Orientation: 5 H
Weight: 4.03 g
Minted under Augustus, Tiberius as Caesar
RIC I (Second Edition) Augustus 246