The As denomination
The As was a bronze, and later copper, coin used during the Roman Republic and Roman Empire.

During the Republic, the as featured the bust of Janus on the obverse, and the prow of a galley on the reverse.

Following the coinage reform of Augustus in 23 BC, the as was struck in reddish pure copper instead of bronze.

The as continued to be produced until the 3rd century AD. It was the lowest valued coin regularly issued during the Roman Empire.

The last as seems to have been produced by Aurelian between 270 and 275, and at the beginning of the reign of Diocletian.
As

(1) A. Terentius Varro II 170-158 BC
Obverse: Laureate head of Janus; I
Reverse: Prow of galley right; (VAL) / I / ROMA
Ref: Crawford 185/1; Sydenham 364
(2) C. Cluvius Saxula 170-158 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right C·S(AX) I ROMA
Ref: Crawford 173/1, Sydenham 360, BMCRR...
(3) C. Sulpicius 103 BC
AE As Sardinia
Obverse: Laureate head of Janus; above, mark of value.
Reverse: Prow right; C•SVLPI above; palm-branch in right field; ROMA below.
Ref: Crawford 312/2
(4) Marcus Antonius 38-37 BC
AE As Achaea
Obverse: M•ANT•IMP•TERT•COS•DESIG•ITER•ET•III•VIR•RPC - Jugate busts of Mark Antony and Octavia right.
Reverse: M OPPIVS CAPITO PRO PR PRAEF CLASS F C - Galley right, below A.
Ref: RPC I 1470
(5) Matienus 180-170 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right; (MAT) / I / ROMA
Ref: Crawford 162/3a
(6) Q. Opeimius 169-158 BC
Obverse: Laureate, bearded bust of Janus. I above
Reverse: Prow of Galley, right. OPEI above, I in right field. ROMA in exergue
Ref: Crawford 190/1, Sear 1111
(7) Rome | Anonymous 211-210 BC
Obverse: Laureate head of Janus I
Reverse: Prow of galley right I H ROMA
Ref: Crawford 085/02 H, Alb. 287, Syd. 1...
(8) Rome | Anonymous 211-208 BC
Obverse: Laureate head of bearded Janus I
Reverse: Prow of galley right, club above I ROMA
Ref: Crawford 89/3; Sydenham 213; sear5 ...
(9) Rome | Anonymous 206-195 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right, Rostrum Tridens above I ROMA
Ref: Cr114/2, sear5 #660, Syd 245;
(10) Rome | Anonymous 206-195 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right, meta above I ROMA
Ref: Crawford 124/03
(11) Rome | Anonymous 170-158 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right I ROMA
Ref: McCabe K1.As.1, related to the Craw...
(12) Rome | Anonymous 170-158 BC
Obverse: laureate head of Janus; I
Reverse: prow of galley right; (PT) / I / ROMA
Ref: Crawford 177/01
(13) Rome | Anonymous 209-208 BC
Obverse: laureate head of Janus; ― / CA
Reverse: prow of galley right, fighting platform decorated with club; I / CA / ROMA
Ref: Crawford 100/1c; Sydenham 309a
(14) Rome | Anonymous 209-208 BC
AE As Etruria
Obverse: laureate head of Janus; I
Reverse: prow of galley right; I / ROMA
Ref: McCabe E1.As.1 (related to Crawford...
(15) Rome | Anonymous 211-208 BC
Obverse: laureate head of Janus; I
Reverse: prow of galley right; I / ROMA
Ref: Crawford 056/02, McCabe D1 (related...
(16) Rome | Anonymous 170-158 BC
Obverse: laureate head of Janus; I
Reverse: prow of galley right, butterfly on vine branch with leaf and grape bunch above; I / ROMA
Ref: Crawford 184/1a
(17) Saxula 170-158 BC
Obverse: laureate head of Janus; I
Reverse: prow of galley right; S(AX) / I / ROMA
Ref: Crawford 180/1; Sydenham 361; Type...
(18) Valerius 170-158 BC
Obverse: laureate head of Janus I
Reverse: prow of galley right (VAL) I ROMA
Ref: Crawford 191/1, Sydenham 356, BMCRR...