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) Augustus
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An AE Semis struck 27 BC-14 AD in Caesaraugusta
Obverse: AVGVSTVS DIVI F, Head of Augustus facing left, wearing laurel wreath

Reverse: CAESAR AVGVSTA L CASSIO C VAL FEN, Vexillum on base; II VIR to left and right

Diameter: 20 mm
Die Orientation: 4 H
Weight: 5.34 g
L. Cassius and C. Valerius Fene(stella?) as duoviri
The obverse inscription translates to "Augustus, son of the Divine (referring to Julius Caesar)"

The reverse inscription translates to "Caesaraugusta, to Lucius Cassius and Gaius Valerius Fene(stella?) as two magistrates to govern the colony
RPC I 311
Roman Provincial (Twelve Caesars)
(2) C. Matuinus Aedile | T. Anicius Aedile
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An AE Semis struck c. 45 BC in Parion
Obverse: female head right wearing stephane; C_G / I_P

Reverse: praefericulum; D_D

Diameter: 14 mm
Die Orientation: -
Weight: 2.7 g
No notes for this coin
RPC I 2259; SNG France 1416
Roman Provincial (Republican Provincial)
(3) Carisa
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An AE Semis struck 100-1 BC in Carisa
Obverse: head of young Hercules left wearing lion's skin

Reverse: horseman galloping left holding spear and large shield; CARISSA

Diameter: 18 mm
Die Orientation: -
Weight: 3.3 g
No notes for this coin
AB-446; Vill-6
Western
(4) Castulo
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An AE Semis struck c. 200-175 BC in Castulo
Obverse: Diademed head right

Reverse: Bull right, crescent above; KASTILO retrograde in southern hispanian script

Diameter: 21 mm
Die Orientation: -
Weight: 5.69 g
No notes for this coin
CNH p. 331, 2-3; SNG BM Spain 1223-6
Western
(5) 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
Roman Imperial (3rd Century Crisis)
(6) Germanicus
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An AE Semis struck 15 BC - 19 AD in Italica
Obverse: Bare head left; GERMANICVS CAESAR TI AVG F

Reverse: Aquila between two standards; MVNIC__ITALIC / PE_R / AV_G

Diameter: 24.5 mm
Die Orientation: -
Weight: 5.4 g
No notes for this coin
RPC I 70; ACIP 3339
Roman Provincial (Twelve Caesars)
(7) Germanicus
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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
Roman Provincial (Twelve Caesars)
(8) Iaitos
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An AE Semis struck c. 241-30 BC in Iaitos
Obverse: helmeted head of warrior righ

Reverse: warrior standing half-left, with grounded spear and shield; IAITI_NΩN

Diameter: 14 mm
Die Orientation: -
Weight: 3.4 g
No notes for this coin
CNS I pg. 383, 4; SNG ANS -
Western
(9) Marcus Antonius
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An AE Semis struck 38-37 BC in Syria
Obverse: M•ANT•TER•COS•DES• ITER•ET•TER•III•VIR•R•P•C, bare head right.

Reverse: L•BIBVLVS•M•F•PR•DESIG, quinquereme right, with three oars and stern ending in boar's head left.

Diameter: 20 mm
Die Orientation: 0 H
Weight: 3.61 g

Provenance: Private purchase (May 2018).

RPC I 4092
Roman Republican (44-36 BC)
(10) Marcus Antonius
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An AE Semis struck 38-37 BC in Syria
Obverse: M•ANT•TER•COS•DES• ITER•ET•TER•III•VIR•R•P•C, bare head right.

Reverse: L•BIBVLVS•M•F•PR•DESIG, quinquereme right, with three oars and stern ending in boar's head left.

Diameter: 19 mm
Die Orientation: 0 H
Weight: 4.92 g
No notes for this coin
RPC I 4092
Roman Republican (44-36 BC)
(11) 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
Roman Imperial (Twelve Caesars)
(12) Rome
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An AE Semis struck 211-208 BC in Sicily
Obverse: laureate head of Saturn right; S

Reverse: prow of galley with corvus right; grain ear above; S / K / ROMA

Diameter: 27 mm
Die Orientation: -
Weight: 12.2 g
No notes for this coin
Crawford 069/03a; Sydenham 310b; Type as RBW 287
Roman Republican (211-146 BC)
(13) Rome | Anonymous
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An AE Semis struck 211-206 BC in Rome
Obverse: laureate head of Saturn right S

Reverse: prow of galley right S ROMA

Diameter: 27 mm
Die Orientation: -
Weight: 18.6 g
No notes for this coin
Crawford 056/03, McCabe G1
Roman Republican (211-146 BC)
(14) Tiberius
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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
Roman Imperial (Twelve Caesars)