Bust right / Single span bridge with fortified tower on each side, statues atop towers, boat moored below

Comment- This reverse is often referred to as the Danube bridge, which Trajan built during the Dacian War period, but the actual bridge depicted on the coin is open to speculation. The bridge across the Danube shows up in a band of relief sculptures on Trajan's Column and is different in appearance to the one depicted on the coins.

Draped laureate bust of the Genius of the Roman People / Bridge with a tower at each end, spanning a river

Comment- I believe that's supposed to be two boats and waves under the bridge.