Issued by moneyer Mussidius Longus during the Second Triumvirate (Octavian, Lepidus, and Mark Antony), the iconography of this denarius at first seems an odd choice: a sewer goddess? Mussidius Longus issued two types with this reverse: one with an obverse of Sol and one with Concordia.
From the Numismatic Fine Arts auction catalog, Julius Caesar and His Legacy; an Auction of Roman Coins, 13 May 1991, p. 8:
"The types of this denarius reflect the notions of cleansing and renewal which were implicit in the mandate of the Second Triumvirate. Sol, the sun god, was one of Mark Antony's patron deities. Ancient myths told of a nightly battle between the sun and the powers of darkness, from which the sun always emerged triumphant. This cycle provided an inspiring allegory for the hoped-for victory over Caesar's assassins.
More obscure is the scene depicted on the reverse of this denarius. It is a shrine that would have been familiar to the coin's contemporaries, dedicated jointly to Venus Cloacina, the patroness of the city sewers, and Concord. Thus is symbolizes both purification-- through in a manner slightly incongruous to modern taste-- and the cooperation between Antony and Octavian."
For more information Venus Cloacina and the history of Rome's sewers, see "A Deity Worthy of Respect" under the Stories heading.
Moneyer issues of Imperatorial Rome
L. Mussidius Longus, 42 BCE
AR denarius, Rome mint.
Obv: Diademed and veiled head of Concordia right; CONCORDIA upwards behind; star in right field under chin
Rev: Shrine of Venus Cloacina: Circular platform surmounted by two statues of the goddess, each resting right hand on cippus, the platform inscribed CLOACIN and ornamented with trellis-pattern balustrade, flight of steps and portico on left; L • MVSSIDIVS • LONGVS around above.
Ref: Crawford 494/42b; Bab. 6; BMC 4244; Crawf. 494/42 b; Syd. 1093a