The north and south mole can be seen on coins of Nero from 64 AD. They are not identical. The one on the right, the north mole, has arches. On some coins of the series there seem to be a temple and a man sacrificing in front of an altar at the end of the left, south mole.
More information about the south mole can be found in the description of the buildings surrounding the harbour of Trajan (nr. 55, Porticus Placidiana).
The south (left) and north mole on a coin of Nero from 64 AD.
Testaguzza 1970, p. 97.