Like other emperors, Trajan used coinage as a way to project his power and celebrate his accomplishments. To that end there is a remarkable amount of similarity among the different denominations of coinage in regard to their legends and their imagery. Coins of all denominations very consistently list the titles of the emperor (the titles varying by the date of the coin), and they almost always contain a profile image of Trajan on the obverse. The reverse sides of coins have much more variety both within and between denominations, but it is not uncommon to see the same image found on different denomination coins from different time periods.
The top coin is a gold Aureus, the most valuable Roman coin, dating from 98-99 A.D. The Bottom coin is a copper As dating from 101-103 A.D. The Aureus was worth the equivalent of 400 Asses, but both coins display identical themes. Their obverse sides both depict a bust of Trajan and contain almost exactly the same inscription: IMP CAES NERVA TRAIAN AVG GERM (the As also contains the initials P M). The reverse of both coins show the Goddess Fortuna holding a rudder and a cornucopia.
Another example, this time comparing a denarius and a sestertius (A Denarius was 1/25th of an Aureus and the equivalent of four sestertii). Again, despite the different denomination of the coins and their time difference in minting both coins share the same image.
The similarities in message and image displayed in the coins above, however, should not lead one to conclude that the denomination of the coin had no affect on the image that was placed on its reverse. Graphs generated from the OCRE database show that the different denominations of coins showed distinct favoritism towards different deities:
As can be seen, the Aureus has a relatively wide distribution of deities represented on the reverse of coins. Jupiter and Genius tied for first at 11.76%, while Victory was third with 9.41% of coins.
Victory was most represented on the Denarius, with 17.3% of all coins. Mars and Pax were next, with 7.2% and 6.4%, respectively.
Victory was also the most common image on the Sestertius, but by a much smaller margin. Victory had 15.2%, while Pax was represented on 13.6% of Sestertii. Dacia was third with 8% of coins.
The As showed the most lopsided result, with Victory found on 37.5% of all coins. The next closest was Fortuna at around 7%. These results are especially striking when compared to the wide distribution found in the Aureii.